Fenway is nice, but I thought the seats too damn close. At 6'4", I had a hard time fitting. Still a must see if you've never been. The time I went, it was the week Ted Williams died, and they had all kinds of stuff up for him.
Of the new parks, PNC Park in Pittsburgh is my favorite. They nailed all the little things there. Clemente was number 21, and the right field wall is exactly 21 feet high.
AT&T Park (SF Giants) has PBR on tap, but there's something wrong about paying 8 bucks for a PBR. However, they also have a Gordon-Biersch there, and yes, they have garlic fries on sale.