Current players

As promised, a look at active players (and players not yet eligible) and their chances to make Cooperstown.
1B
Jeff Bagwell
Bagwell is, in my opinion, easily one of the 10 best first basemen ever, and he's approaching the top 5. Gehrig, Foxx, McCovey, and Murray are ahead of him. But who else? It's pretty hard to argue Killebrew or Palmeiro or someone like Roger Connor or Dan Brouthers ahead of him. Bagwell's overall numbers were severely deflated due to the fact that he played his best years in the AstroDome, a significant pitcher's park. Of course, he has been lucky enough to move to a hitter's park in his declining years. But Bagwell's been awesome. He is the best first baseman of his time. He wasn't quite as good as Frank Thomas at his peak, but then Bagwell's been much more durable and consistent than the Big Hurt.
Bagwell won the MVP in 1994 and possibly deserved it in 1996 and 1999. In '96, Bagwell hit 461/750/368 in the AstroDome to put together one of the best non-Bonds seasons of the past 20 years. But Ken Caminiti was "clutch" for the Padres and won the MVP (steroids and all).
Bagwell hasn't always been perceived as a Hall-of-Famer, but I would argue that this is the fault of the people doing the perceiving. I once heard a baseball announcer say that if you have to think about a candidate, they're not really a Hall-of-Famer. Well, isn't that sound advice! Go with your first impression, no matter how stupid, uninformed, biased or misguided it may be. Hopefully, the voters will see Bagwell as the offensive juggernaut he was and put him in on the first ballot.
Frank Thomas
Thomas is a tough case. He's actually similar to Ken Griffey, Jr.; a sure-fire Hall-of-Famer until the injuries came. But I'd say that Thomas was a better player than Griffey at his peak, even considering defense. He's one of the ten-best first basemen of all time, and his run from 1991-2000 was as good a 10-year stretch as any AL player has had in years. The injuries have cut his career short, limiting his playing time in recent years. But I would argue that when you look at Frank's career as a whole, he is still a Hall-of-Famer.
Rafael Palmeiro
Well, isn't this a hairy question? Mark McGwire now looks positively dignified when compared to Raffy. At least McGwire didn't perjure himself and try to blame a teammate. It's very unclear as to what extent steroids played in Palmeiro's development. We really have no idea when he started using them and for how long.
After Palmeiro got his 3,000th hit, I argued that he was a Hall-of-Famer. And based on the numbers, I still think he is. Skip Bayless wrote an article for espn.com advancing the preposterous argument that because Palmeiro didn't inspire fear and awe, he shouldn't be in the Hall of Fame. I'd say that Mr. Bayless has no idea who is actually in the Hall of Fame. Because when you look at the actual inhabitants, you realize that Rafael Palmeiro is no insult to the institution that inducted Freddie Lindstrom, Chick Hafey, Tommy McCarthy, and Candy Cummings. The idea that players like Willie Mays are the standard has never been the case. Players like Mays and Ruth are the elite. The average Hall-of-Famer is someone like ... I don't know, Harmon Killebrew or Hal Newhouser. And Palmeiro compares very favorably to them. Palmeiro is sort of like the hitting version of Don Sutton; he was never amazingly good, but he was really good for so long that he earned a spot in the Cooperstown. Based solely on his numbers, Palmeiro is a Hall-of-Famer, with no doubt in my mind.
Then came the stanozolol. How do we factor this into the discussion? I refuse to dismiss Palmeiro out of hand. It's the self-righteous thing to do, and it's done by people who don't want to spend time thinking when they could be out judging people. The only thing we know for sure is that Palmeiro tested positive this year. It's possible (though admittedly not likely), that Palmeiro didn't start using steroids until recently. It wouldn't be out of the question at all to assume that Palmeiro used steroids to bolster his declining career in order to get 3,000 hits and reach Cooperstown. We don't know for sure what he tested positive for (the stanozolol report has never been confirmed), and we can't say for sure that the steroids actually made him a better player (everyone assumes this to be true. While steroids do enhance certain physical aspects such as recovery time, that doesn't automatically make someone hit for a higher average). And we must also face the fact that steroids weren't even outlawed in baseball until recently. So the issue becomes much more difficult the more we think about it (which is why the talking heads on TV don't like to think).
My personal opinion is that our limited knowledge of Palmeiro's steroid use is enough to disqualify him from the Hall. I say this with grave misgivings, especially since we cannot be sure that anyone we enshrine in the next 20 years is steroid-free. We cannot focus all of our vitriol upon Raffy just because he got caught while unconsciously giving others a free ride to do the same thing.
But Palmeiro is, I believe, a fairly borderline case for the Hall of Fame. So much so that this little steroid issue is enough to raise a reasonable doubt towards my inducting him into the Hall. The good thing is that we don't have to decide now; we have five years to learn more about Raffy and his peers and make a more reasoned decision. But given what I know now, I just don't think we can let Raffy in.
Mark McGwire
Retired 2001; Eligible for Hall December 2006
I think Mark McGwire is a Hall-of-Famer. Now I'll try to defend myself from the charge that I'm a flip-flopper with a double standard.
First of all, McGwire never got caught using steroids. There has never been any conclusive proof that he used them. Yes, we all drew the same conclusions from his Capital Hill testimony, but the simple fact is that if we know the bare minimum about Palmeiro, we know absolutely nothing about McGwire. We don't know how often he used, or when he used it, or even what he used. He may have been a grievous offender, or he may just been a small-time dabbler. We will never know. The most important issue to my mind is that McGwire's alleged steroid use occured before baseball outlawed it. The oft-repeated saying about Pete Rose is that Rose wasn't banned because he gambled; he was banned because he broke the rule against gambling. But, unlike Palmeiro, Mark McGwire never broke any MLB rule against steroids, because no such rule existed. So McGwire may be guilty of chicanery or a minor federal drug law, but seeing as he retired in 2001, he could not have broken baseball's drug policy.
Am I splitting hairs? Perhaps I am. But I refuse to automatically hate, disdain, and turn my nose up at every steroid user. Those who think that steroids are bad, and therefore everyone who uses them is just plain bad, lives in a fantasy world of Care Bears and Dick and Jane. The real world is much more complicated, and people are much more complicated. We can say with some certainty that both McGwire and Palmeiro are steroid users. But, as far as we know, that's where the similarity ends. Palmeiro violated MLB's substance abuse policy and then perjured himself; McGwire did neither. Palmeiro blamed a teammate; McGwire didn't. Palmeiro is a marginal Hall-of-Famer; McGwire is not (in my opinion). Palmeiro used (if the source can be believed) stanozolol, a powerful anabolic steroid; we don't have a clue what McGwire used, except for andro, the supplement that was perfectly legal at the time. Every aspect of the question favors McGwire rather than Palmeiro. And that more than anything is why I think that Mark McGwire is still a Hall-of-Famer.
Will Clark
Retired 2000; Eligible for Hall December 2005
Nobody has any love for Will. Which is too bad, considering that he spent his prime years in a pitcher's park and hit like few people ever have. Clark's 1989 season, where he hit 412/546/333 in a very unfriendly park, is one of the best seasons of the past 20 years. But the ignorance of the voters was exposed when they gave the MVP to teammate Kevin Mitchell.
Clark's talents were never fully appreciated. He had several truly great years in San Francisco, and then had good years for the rest of his career. He finished with a 384/497/303 career hitting line, compared to the 335/410/266 league average. He was also an above-average first baseman. It's a tough call, I msut admit, but I think Will belongs in the Hall. Just because no one thinks of him that way doesn't alter the essential truth.
Jason Giambi
Well, back to the steroids. There's no chance that Giambi will make Cooperstown, and I don't think he'll probably earn it either. The steroids are a hairy question here, too, since we can't give much credit for Giambi's hitting to them. It's entirely possibly that they didn't help him a bit (Giambi didn't think so). But, steroids or not, it doesn't look like he'll ever regain the form in Oakland that made him, for a short while, the best baseball player in the world not named Barry.
Jim Thome
Thome is a different question. While Thome doesn't have seasons quite as big as Giambi's, he does have a very impressive career and no steroids casting a shadow over it. Thome was one of the 10 best hitters in the league pretty much all the way from 1995 to 2004. His 2002 season was likely his best, but he was the second-best player in the league behind Giambi. Thome will have to regain his good hitting form again to fight his way into Cooperstown, but I think it's entirely possible that he'll earn his way there. But I don't see him actually getting elected; baseball men don't like 1-dimensional players (even though Thome isn't 1-dimensional, but that's a whole other rant...).
Carlos Delgado
Look at what Delgado's done over his career, and it will surprise you. The knock against him is that he's been in a hitter's park in the AL for his whole career, and he's worthless on defense. But I think he's one of the 5 best hitters of the 1990s, and if he finishes out his career well, he might just be worth a plaque. But he won't get one, for the same reason Thome won't. People have already made up their minds, and they have far too much pride and bluster to admit when they're wrong.
John Olerud
People probably don't realize what a fine career John Olerud has had. He's had two near-MVP seasons, in 1993 and 1999. He was the best player in the AL in 1993, but Frank Thomas won the MVP. Olerud has been a darn good player for one heck of a long time. He wasn't as popular as someone like Mark Grace, but he actually was a better overall player. He's no Hall-of-Famer, but he's better than people give him credit for.
Mark Grace
Retired 2003; Eligible for Hall December 2008
Grace was a good player for quite a while. But he was never great, and it wasn't quite as long as people think. He did have more hits than anyone else in the 1990s, but that's an accident of history and no argument for induction. Just because somebody else got all their hits between 1985-1995, Grace gets more credit for putting it together in an even decade?
Future Prospects: Todd Helton, Albert Pujols
2B
Craig Biggio
Biggio is, after Barry Bonds and perhaps Roger Clemens, the best baseball player still active. He has been an excellent hitter, a solid defender, and a master of the "little things," such as SBs and HBPs. The AstroDome hurt him as it did Bagwell. But Biggio stands a chance of making it to 3,000 hits, whereupon he should get in on the first ballot. He deserves it, because only 5 second basemen in baseball history were better.
Roberto Alomar
Retired 2004; Eligible for Hall December 2009
It's too bad that Alomar's career crashed to a halt when he went to the Mets. But I feel that, even before his career died, he put together enough of a fabulous run to make the Hall of Fame. He's one of the best-hitting second basemen ever, and he had the great defense to back it up. As it is, he's just behind Biggio all-time.
Jeff Kent
Kent is an odd case; he didn't have a really good season until he was 29 and didn't break out with a great year until age 32, when he won the 2000 MVP Award. Do I think he belongs in the Hall? It's a tough choice, but I think so. Kent has put together a good combination of really strong offense and good defense. He's managed to keep performing well at an advanced age (his 2005 season was one of his best), and he is the all-time HR leader among 2B. If he has another couple good years, I think he'll get in eventually.
Chuck Knoblauch
Retired 2002; Eligible for Hall December 2007
Remember him? Knoblauch was a Hall-of-Famer, without a doubt, from 1991-1999. After the 1999 season, Knoblauch was just 31 years old, had won 4 World Series rings, and had never had a bad season in his career. It looked like nothing could stop him from getting to Cooperstown.
But Knoblauch's career died a sudden, tragic death. Everyone remembers Knoblauch's trouble throwing to first; few remember that he stopped hitting, too. But Knoblauch soon became a bad-hitting left fielder, and he retired after a year in Kansas City at the age of 34. Sure-fire Hall-of-Famers don't just stop hitting and fielding at the age of 31; it just doesn't happen. Except that it did happen to Knoblauch. He wasn't able to complete his Hall-of-Famer career, and I still have no idea what caused it.
The only other active second basemen with careers of any note are Bret Boone, Ray Durham, and Mark Loretta, and they're a few light years away from Cooperstown.

Seeing as this is taking longer than I imagined, I'll split it up into parts. I'll be back with the shortstops and third basemen tomorrow ...