*stretches fingers* ok, the length of this post will be determined by how much free time I have
Castlevania - SotN obviously, but also Lament of Innocence and Curse of Darkness, as far as Michiru Yamane's stuff goes. But I like a lot of classic stuff just as much. The recent wiiBirth of Castlevania Adventure had awesome tracks. Pretty much any track from 1 to 3 is great too, especially Castlevania 2 (Dwelling of Doom!). Not to mention Dracula X's Bloodlines, pretty much my favorite Castlevania tune (and which lead to the awesome remix at the end of SotN and the violin intro in Castlevania 64, two of my most listened-to Castlevania tracks).
Mega Man - some stuff from the classic NES stuff, like 2, 3, 4, 7, and 9 (havent gotten around to 10 yet), but personally I'm into the X series. I pretty much like anything from X to X8 and Command Mission, but less-so after X4. The Zero series also had some amazing stuff.
Ys - if you love classic Castlevania or Mega Man X music, you owe it to yourself to check out Ys music too. The games themselves are just as awesome, especially Oath in Felghana. I prefer Ys games on PC, but you can get Ys Book I and II on Wii's virtual console, Ys VI Ark of Napishtim and PS2/PSP, and Felghana is coming to PSP soon. Nihon Falcom's in-house music group has been one of the most famous in gaming, right next to (or even more-so than) SNK's old one.
KOF - the SNK Shin-Sekai Gakkyoku Zatsugidan days
My favorite is Good Bye Esaka, but also Bloody, Tears, Mad Fantasy, Rhythmic Hallucination, Fairy, 176th Street, Blue Mary's Blues, KD-0079, W.W.III, Fanatic Waltz, Rumbling on the City, Wild Party, Crystal, Will, The Trooper, Inner Shade, Geese no Katakori, and Requiem in D Minor K.626 Dies Irae. I Also REALLY love Toshikazu Tanaka's music in the MI games, I feel they're pretty overlooked/underrated. They're no SNK Shin-Sekai, but they're not trying to be. They suit the silly, crazy fun of the MI games, and are generally just really exciting tracks. I like most of his stuff, actually. I mean, look at Matrimelee, the guy was great. I wonder what he's up to now. The new stuff I've heard on the official XIII site sounds great too. I'm kinda sad I spoiled myself listening to them so soon before being able to play the game. It sounds like EVERYONE's music is awesome this time, which not even old SNK was able to do for me. Still, the new stuff is not at the old SNK quality yet, not for me at least, but it's close. It's tough competing with something like Good Bye Esaka though
Soul Blade Khan Super Session - this is honestly the only Soul game soundtrack I like really like to listen to outside of the games
I love Meditranian Call, Another Fanatic, The Edge of Soul, and An Oath of the Sword.
Lufia/Estpolis series - pretty much every track for Lufia FoD, Lufia II: RotS, and Lufia The Legend Returns
F-zero - Most of the tracks from the first game and F-zero X, and even more the Arranged Guitar Remixes! I also like some F-Zero GX tracks
Super Monkey Ball DS and Banana Blitz (I hate the later game, but it remixed the SMB DS tracks to sound even better)
Tekken - Tekken 2 has my favorite music in the series, almost every track is awesome. Tekken Tag Tournament has the 2nd best OST. I'm not too fond of Tekken 3's stuff beyond Jin's and King's tracks, and I can't remember anything for 4. 5, Dark Resurrection and 6 have quite a few nice ones (and a few horrible ones too), especially Moonlit Wilderness, Snow Castle, and Anger of the Earth and Fallen Colony, respectively.
Zelda - A Link to the Past is one of my most favorite soundtracks ever. Every track is still as magical to me as it was the first time, and in some cases more today. Hyrule Castle is probably my favorite out of that, but for a long time it used to be Dark World. OoT has some good stuff, like the Windmill Hut, Gerudo Valley, and the final battle with Ganon. Windwaker is my 2nd best to LttP, especially with tracks like Dragon Roost Mountain and Molgera battle. Majora had it's moments. I didn't really like anything from TP. Link's Awakening had Mt. Tamaranch and Tal Tal Heights. The GBC and GBA games had good stuff too. I like some Adventure of Link stuff, but I think mostly out of nostolgia. I havent been able to play enough of the DS games.
Mario games - Super Mario Bros 3, Super Mario World, and Mario 64 have the best tracks here. Especially Mario World. Sunshine and Galaxy had some nice stuff too. I've always hated how the Space Junk Galaxy theme was used in only one, easy, short world while Honeyhive Galaxy got two :| Yeah, I'm not as in love with the game as most people. Haven't picked up Galaxy 2 yet. Mario Land for GB has the Underground theme, which I'm glad SSBB has recently popularized.
SSX3 - one of the only soundtracks made up of liscenced music that I like. I'd never heard any of the music outside of the game before, though.
Kinetica - some good stuff, I really liked the intro theme especially
Super Smash Bros series - too many to name, ofcourse (especially considering the epic scale of the Brawl soundtrack)
Metroid - anything from the 2D games. From Prime, I like Phendrana Drifts and the opening/credits theme a lot (not to mention the updated Magmoor theme). Prime 3 had some good ones too. Can't remember anything specific from P2 besides the new version of the Maridia theme, maybe the title music.
Guilty Gear and Blazblue - Awe of She! Some other good ones are there too, though. I liked most tracks from Blazblue
Street Fighter - too many. The entire SSF2 soundtrack still rules. I even like a ton of SFEX series tracks (even EX3 has one really good original track - Ancient Zone). I used to not care for any Alpha 2 music, but now some of my most favorite tracks are from it, like Akuma's, Gen's, Adon's, Cammy's, the epic Field stage (SF2 TAM!), Ryu's 2nd ending theme, and especially (and strangely) Bison's/Vega's ending theme (that and Akuma's theme were basically my soundtrack for when I went to India in January of 2009). Alpha 3 has some good ones too, like Vega's (claw), Rose's, Karin's, and Evil Ryu's... but I found most of the others too dull. I also really like the SF2 animated movie ost... the US version
some of the liscened stuff, but also the original stuff (fun fact - the composer also did the theme for Baywatch
Lets Tap - the music game is enough reason to play this game... quality Sega stuff here
MvC - I just like the Strider, Chun-li, and Roll (vocal) themes. Don't like anything from MvC2.
TvC - for me, out of all the crossover fighters I've played, this one has the best OST over all. I mean, the credits theme is Orpheus In The Underworld (AKA The Wacky World of Tex Avery theme, AKA that song in one of the New Mini Wheats commercials)!!
the Bust a Move (Puzzle Bobble) theme
Batman for NES - any track. Even the game over theme was epic.
Super Adventure Island II - pretty much any track, especially the snow/ice stage
Mystical Ninja 64 starring Goemon (I AM IMPACT!)
Earthbound (Mother 2) - so many... the bicycle theme comes to mind right away
Kirby - everything, especially the SSB remixes
Parasite Eve - Main Theme Orchastrated, Primal Eyes, Out of Phase, Kyrie, Wheel of Fortune, Influence of Deep -CM Version-
Zone of the Enders - Kiss Me Sunlights, Flowing Destiny, Beyond the Bounds, ALOIVIA, Zakat, and even one or two from the anime and film
Top Gear Rally - Main Menu Theme, Desert, Jungle. Also, some Top Gear and Top Gear 2 tracks too.
Killer Instinct - the Killer Cutz sondtrack (though it's been a while), and some Gold stuff too, like I especially remember liking Gargos' theme (reminds me of an episode of Reboot)
the Rad Racer theme - when that theme hit up, you knew you were getting somewhere
Double Dragon main theme
Strider theme (and the new arrangement for Strider 2)
River City Ransom theme. no better music can make you feel like a delinquent.
ok, thats enough for now...