The Common Man's buddy Bill brought this all up last week, in his examination of Jeff Bagwell (who comes in at #4 among 1B) and Frank Thomas (#10) and comes to the conclusion that Bagwell was the better all around player (which was James' conclusion as well).

This prompted some confusion for The Common Man, who couldn't mentally get past Jeff Bagwell as the 4th best 1B ever. In the comment section, he wrote, "I love me some Bill James, but we've got to be able to find four better 1B than Jeff Bagwell, can't we? I can't quite wrap my mind around him being an inner circle HOF guy." Bill responded and effectively challenged that, pointing out a lack of candidates to unseat Bags. Gehrig and Foxx are obvious. James puts McGwire at #3 (Bagwell probably moved past him with three good years after the publication of the book). After Bagwell, James has Eddie Murray at #5, Johnny Mize (6, much more reasonable than The Common Man figured, after looking back). Harmon Killebrew was #7, Hank Greenberg is 8, and Willie McCovey is 9. Nobody really stands out as better than Bagwell.

So, at this point, the question for The Common Man becomes, where does Pujols belong on James' list? Assuming that no one else is added from this era (yet, though Morneau, Ortiz, Howard, Fielder, Helton, Giambi, Konerko, Thome, Delgado, and Teixeira may have something to say about it already), where can we safely slot Pujols among the greatest of all time?
It's pretty clear to The Common Man that Pujols should already be in the top 12. Given the troubles with assessing 19th century players (which The Common Man has gone into before, he would err on the side of caution with players like Cap Anson (who is #11 for James). And Don Mattingly (#12, James' worst choice in the book), with respect, is not fit to carry Albert's jock. Given the defensive upgrade, and the peak value, and the fact that Pujols has created about 65% of the runs in 55% of the plate appearances as Thomas has, Albert probably edges ahead of The Big Hurt at #10.
McCovey's three best seasons ('68-'71) stack up with the best of Pujols' work very nicely. That said, the body of Pujols' work outside of those years is far less impressive. Stretch has an OPS+ of 146 before those three years, and 126 after. Pujols' lowest single season OPS+ is 151. The sheer dominance of Albert is too much to ignore here (note, Thomas probably also shoots past McCovey).
Hank Greenberg, at #8, is a tougher case. His counting stats (1628 H, 331 HR, 379 2B, 1276 RBI, 1051 R) are remarkably similar to Pujols' (see above). And Greenberg suffers from losing four years in his early 30s to military service. Just because he's 29 though, and still going, and is already marginally ahead of Greenberg, The Common Man's gotta push Albert up past him.

Johnny Mize is a tough call too. His peak is comparable to Pujols, but it's shorter and not easily bunched together. That said, Mize missed his 30-32 seasons to WWII, which would have presumably extended that peak, helped his overall counting stats, and raised his OPS+. We don't have advanced defensive stats for Mize, but his reputation preceeds him, as one of the sweetest fielders ever around the bag. It's probably fitting that, until Pujols does more to assert himself, he stays right about here. Call him #6b, and Mize #6a.

There's little doubt that Pujols will move past The [Original] Big Cat soon, perhaps by the end of the year. And depending on how you feel about Mark McGwire, he could be sneaking up on #4 as well. Eddie Murray probably is safe for another season or two, which means that Bagwell's ok for now. But with, presumably, 5 more prime or just-off-prime seasons left to go, and maybe another 3-5 beyond that, it's likely that Pujols will move into the top 3 all time before he's done. Whether he's actually able to push aside the twin colossuses of Gehrig and Foxx will be fun to watch.