Well, this is simple. Since there are a lot of bands or musicians that only do music for games, it would be cool that you mention bands or musicians from games that you like. Example: I like a lot Econoline Crush from the PS game Sled Storm, Saki Kaskas from various Need for Speed versions, and obviously the VRock station form GTA Vice City. You can mention only the game if you want to, since not all the games have music credits.
The Final Fantasy series has always been a big favorite of mine when it comes to video game music (my favorite song will always be "Dancing Mad"). But as recently as early 2009, I have been absolutely captivated by the music from a series of games called Touhou. Each song is amazing in its own right, but what's truly amazing about it is that every single song of every installment in the Touhou series was composed and recorded by one man: ZUN. If I had to choose one song from that catalog as my all-time favorite, it would have to be this:
The soundtracks to the Castlevania games I would actually consider among my favourite music in general, especially the stuff composed by Michiru Yamane. Have the Symphony of the Night soundtrack on CD, and the artwork is more badass than most of my metal collection!
Anyone ever heard the soundtrack to Castlevania: Judgement? Easily the worst game in the series, but has some fantastic (and often metal as fuck) remixes of lots of Castlevania tracks, same can be said about Harmony of Despair, except that game doesn't suck.
HoMM III soundtrack is supreme, just supreme. HoMM IV might be a game not worthy of having that name, but Paul Romero did a great job in that case too.
Why thank you kind Sire! I had to stop myself from flooding it with all manner of songs as the moment I started posting I recalled many awesome ch00ns.
Probably my favourite track from Legend of Dragoon:
Oh, and I dunno why I didn't post this before: simply the greatest boss battle theme to any game ever. EVER.
And the regular battle music is essentially a violin version of it and is also kick-ass:
And there's also a third version of this tune, again with guitars. Not as cool as the first one I posted but some people would say otherwise. Not sure when this is used, probably another boss theme:
I like a lot of the Nintendo stuff. Obviously Zelda games have some nice classics like Gerudo Valley, I also really like Kirby stuff (Green Greens, Dreamland), and Donkey Kong stuff is awesome too.
As for licensed soundtracks, there's not many really good ones in my opinion, but some of the Tony Hawk games have had good songs in them (such as Seed by Sublime in THUG). I heard Splatterhouse has a good licensed soundtrack as well. The Haunted are on it, I know that. And how could I forget, Brutal Legend's soundtrack.
Finally, the music in Shadow of the Colossus is some of my favourite. Epic, mysterious, atmospheric, amazing stuff.
Also, I just finished Bastion (action RPG). Story was kinda meh, but the presentation of the game was absolutely brilliant. I mean, I was very impressed, seeing as how it's a downloadable title and all. And the soundtrack is so much win.