This guy has been to every major league ballpark (quit drooling). He's got a review of the two new parks in Philly and San Diego, and his ranking of all the current ones, pretty cool stuff.
I haven't been to many, because I've been holed up in the northeast my whole life, but I'm going to try this summer to hit up Pittsburgh, Cincinnati, maybe Detroit, Milwaukee too. Here's my short ranking of the ballparks I've been to:
1. Fenway
2. Wrigley
3. Busch Stadium
4. Comiskey
Curt