Let's see...

-Zelda games don't exactly have the best music, but the best music that suits the game and whatever your doing. That and it's theme song rules.

-MGS games. The first and third one had amazing scores, end of discussion. The second only had good music during the cutscenes.

-Final Fantasy music. Made by the god of gaming music, Nobuo Uematsu himself.

-Star Fox`Adventures. Don't know about you, but I really liked the moody music.

-Ninja Gaiden has a really good OST. Some tracks just don't cut it, but the rest is awesome.