Fenway, Old YS, New YS, Shea, Camden, Nationals, Citizens Bank, Wrigley, US Cellular, Turner, Safeco, Coors.
Been to each of them once, except Fenway (a lot) and Camden (5ish).
On MeanWalrus' note, the most memorable games I've been to are: Game 5 of the 2004 ALCS, Game 1 of the 2007 WS, Game 4 of the 2003 ALCS, Dice-K's first game at Fenway (against Felix Hernandez, too), and a game in 2001 (maybe) when Scott Hatteberg hit a grand slam and hit into a triple play. That has to be the only time that's happened, right?