Both No More Heroes OSTs. One of 'em is called Dark Side Mode, which is a bunch of remixes done by random artists.
Eternal Sonata, Shadow of Colossus, MGS, FF, Zelda etc., there are a lot of brilliant pieces in a lot of games and I couldn't possibly pick a favorite.
Legend of Zelda (no doubt), The World Ends With You, and for some reason, the soundtrack for Donkey Kong Country 2 just sends chills down my spine...
Hm, I'd definitely say Metal Gear Solid(Doesn't matter which one >_>). I mean I've seen people who listen to the soundtrack, not knowing what the game is lol.
I've only just started Higurashi no Naku Koro ni Kizuna, but I already love the background music. It sets the mood perfectly for just about every situation (it's a visual novel, so you don't do much -- therefore a crappy soundtrack would detract from the game a lot more than most, as it stands out a lot). Everything from the funny school scenes to the horror has a piece of music, and they fit wonderfully. Oh, and I also love the game's theme...=P. I've always adored the music from Kingdom Hearts, it's composed very well and has some pieces that sound like they came straight out of an epic or something (i.e., Destati). And I'm kinda surprised; I would have expected to see more people mention Final Fantasy, which is known for its notable scores... That and the .hack//G.U. series, ohhh geez...While a lot of the field background music isn't too notable (it's good but not amazing), the openings and some areas -- The Lost Grounds, especially -- have some absolutely gorgeous choral and instrumental music. Many of the character themes are like this too, and there's also some very nice piano music in there. The Ace Combat 5 OST is pretty good, too, although I haven't heard too much of the soundtrack alone and I haven't finished the game. And I'm surprised not to have seen anybody list Halo yet, seems like kind of a no-brainer. I don't even have to explain why Halo's soundtrack is good. Really, it's impossible to pick a 'best OST,' because there's so many good ones and it depends on your musical tastes =/.
Hmm, I like quite a few a lot. Devil May Cry 3, Metal Gear Solid any of them were good, FF6, FF7, FF8, Legend of Zelda, Kingdom Hearts, Chrono Trigger and Cross. Those are the ones that come to mind any way at the moment.
FFX OST was just beautiful... anybody who played will remember songs like "To Zanarkhand" for the rest of their lives.. Any Zelda games have good OST's as well.. and KH, naturally :3