I've been to a few stadia all over, but there are two that stick out to me (that I haven't seen mentioned here):
Reliant Stadium/Park, Houston, Tx, USA- I went to a Mexico/Colombia Gold Cup game here, the facilities were beautiful and the atmosphere was great... and there was nothing like seeing the Mexicans leaving dejectedly after being eliminated from the tournament by a NASTY chip from about 40yds out to win.
Estadio Azteca, Mexico City, Mexico D.F., Mexico- I saw Club America play @ Azteca- I don't remember much about the game, but I will NEVER forget the fact that there were 107000 rabid fans watching the match with me.