I think OP got it right: Frank Thomas. I'm only 24, but I don't think there's been a better all-around hitter since Ted Williams. I won't comment on Pujols, as I rarely watch the National League.
Since its hard to compare pitchers and hitters, I'll mention Maddux, too. Not sure if he's necessarily the best pitcher I've ever seen, but he's the best pitcher I've ever seen considering his relative physical prowess and athletic ability.
As a White Sox fan, Mark Buerhle reminds me of him, except about three levels below him.