My favourite composer is definitely Nobuo Uematsu. I don't know anyone else who can transport such amounts of atmosphere in his music. The soundtacks of Final Fantasy 6-8 will always be in the top region of my personal game music hitlist. The midi-sound has its own charme, too. ^^
His songs are brilliant in the games, but when you hear them live, played by an orchestra, it blows you away.
I think, it was two years ago, at the opening concert of Games Convention in Leipzig. They played "Dancing Mad", the Boss Fight song of FF6, with organ and choir and all. Never heared something like this before. Just amazing.
Though his music is really great, I like other soundtracks, too.
Turning to western games, the music from Startrail and Shadow over Riva is also very good. As well as Drakensang's. I'm listening to the CDs time by time. Never gets boring.
There are other games, like Divinity, Witcher, The Settlers 2 (new and old version), etc. where I like the music. They are just too many to remember them all and list them.
But I agrre, music is one of the most important part of a game. The best story and greatest atmosphere doesn't help when there's no good music, that can bring it over to you or in worst case destroys all of it.