Anything from Katawa Shoujo. Rocket Jump Waltz TF2 soundtrack. Oh, also Terraria music.

http://www.youtube.com/watch?v=d3gLNomXwlw

Personally I enjoyed the music from a game out in the 90s called Wargasm. Nothing like blowing shit up to the sound of massive choral arrangements. :D

http://www.youtube.com/watch?v=lMktFQhBMTg

the soundtrack of saya no uta is so fucking good it hurts

http://www.youtube.com/watch?v=G_80PQ543rM also THE FUCKIN MOON

http://www.youtube.com/watch?v=WQbOAEP-vgM FTL soundtrack is ballin

http://www.youtube.com/watch?v=gFaTP4FoRfU probably favorite boss music ever (isaac)

https://www.youtube.com/watch?v=8RtLhXibDfA

https://www.youtube.com/watch?v=tBWl9p0fH28&t=114

Free Space 2 (just yt freespace 2 music) tons of songs so I wont list them.

I'm actually listening to the hotline miami soundtrack in my car nowadays - it's damn good.

http://www.youtube.com/watch?v=9QyQ9PsOj6A

From one of the best games made. Command and Conquer. Red alert

portal: still alive
portal 2: want you gone
the first i can remember

legend of dragoon had some of the most inspirational music ever
http://www.youtube.com/watch?v=-B8M8s2Y2yQ
still gives me the goosebumps

Pretty much all of The Elder Scrolls music.

Morrowind: http://www.youtube.com/watch?v=W-UZ3i5pYW4

Oblivion: http://www.youtube.com/watch?v=8H7KoAK0twI

Skyrim: http://www.youtube.com/watch?v=7XdRyReG3QE

Fallout New Vegas
Fallout 3
Pokemon Ruby/Sapphire
Battlefield 2
Call of Duty: Finest Hour

now for COD, this was like the rip off release of COD 1 for the PS2. I absolutely loved this game and the rest of the PS2 releases of the games aswell (which I think ended at COD 3). I think the music was really done well and captured the energy of a battle.

http://www.youtube.com/watch?v=RwF7_gfhoqU

F-ZERO
Super Nintendo

Game Over

Silence is better.

No mention of Final Fantasy Tactics?

One sample of the 20+ battle themes, with the playlist of all the songs
http://www.youtube.com/watch?v=lGdeHJKicmc&list=PL199E3C72F464C304

Bastion. All of it, but more specifically:

http://www.youtube.com/watch?v=xzGEiER7mkc

if no one said bomberman hero then yea bomberman hero

http://www.youtube.com/watch?v=qutUyQqhjdM

Half life 1, 2 and EP1/2 Soundstrack.
Basically anything made by Kelly Baily

One of the best mixs out there for his entire soundtrack

http://www.youtube.com/watch?v=DW9spBlsejo

Zelda - The 'Windmill Song' (Song of Storms)
No lie, actually made it 4 hours into this.... :|
http://www.youtube.com/watch?v=KeIVybmTgWg

Ctrl-F "World of Goo"

C'mooooon!

http://www.youtube.com/watch?v=twB8ZwpZxQM

Paper Mario: TTYD

http://www.youtube.com/playlist?list=PL1lerSPdP8Q9MbH75FZB_KsUrW6xHtirj

Based GotYAY has some great music (full playlist above).

http://www.youtube.com/watch?v=59eyIkPZt7g
http://www.youtube.com/watch?v=1GxDcbMBi50
http://www.youtube.com/watch?v=40RtEtwzHCw
http://www.youtube.com/watch?v=iI7j968mes0

http://www.youtube.com/watch?v=bXpOB7IatQw

Actually, I think my favorite game music is Turok: Dinosaur Hunter, but mostly because of the speedy percussion within most of the tracks.

Ancient City
http://grooveshark.com/s/Ancient+City/3Z0ZYA?src=5

Guile's theme song.

banjo kazooie, diddy kong racing, secret of mana, epic fantasy battle, and alot more games, WoW has alot of great tracks aswell.

10/10

http://www.youtube.com/watch?v=JaVdxMYUaZM

Shadow of the Colossus

http://www.youtube.com/watch?v=bFqXM-t2yss

san andreas

Fifa ofc

I don't know if this has been posted or not yet, but for those of you who like animal crossing:

http://tane.us/ac/

That will update every hour, based on your computer's clock, and play the AC/WW/CF/NL song that corresponds to your time, on loop. (You can pick which game's soundtrack you listen to)

As for music, I'm a big fan of David Wise's stuff.

http://www.youtube.com/watch?v=Z8boRM6xRXg - Star City

http://www.youtube.com/watch?v=1IDudDgfcgQ - Stickerbrush Symphony

And a few others:

http://www.youtube.com/watch?v=oESlnJtSfP0 - Paper Mario Miniboss Music

http://www.youtube.com/watch?v=-uInmFU6JkU - Lost Woods

http://www.youtube.com/watch?v=Hy0aEj85ifY - Gerudo Valley

Metal Gear solid for obvious answer. I also really liked Frozen Synapse soundtrack.