You haven’t lived until you’ve heard the dark, moody, and mysterious soundtrack from the Thief series. 
Some of the greatest ones have already been mentioned. Here are some more 
Super Metroid (SNES) ost:
http://www.youtube.com/playlist?list=PL0BCE0BA953AC33E4Shadowgate (NES) full ost:
http://www.youtube.com/watch?v=MZfpM7Ej6lIKirby’s Epic Yarn (Wii) Full ost:
http://www.youtube.com/view_play_list?p=0F49F13EA649773BDoom (PC) full ost:
http://www.youtube.com/watch?v=QJzveo6IBsU&playnext=1&list=PL486598CA3D288F41&feature=results_mainSonic 2 (Genesis) ost:
http://www.youtube.com/watch?v=-LYB7iLZNWEAnd of course, theres this bit of classic video game opera…. (warning: tasteless humor and swearing)
http://www.youtube.com/watch?v=MBxSMnYCPjwKatamari Damacy!
I agree about the Legend of Zelda soundtrack as well. There’s one particular very simple but wistful theme that plays in Ocarina of Time when you go into the windmill that still gets stuck in my head though I haven’t played the game in years.
I like the music from Sims 
JuanFrancisco said
I like the music from Sims![]()
Hahaha, what a coincidence, just listening that.
Medieval is my best, but the others are pretty much cool, too.
KRAKOUT for C64
Everyone played this game to listen it’s unique music.
This is an old thread but as I see it is bumped and one of the best soundtracks is not mentioned yet, I felt like I should mention “the best soundtrack ever”.
Does anyone here remember “Outlaws” ? In my opinion, it is one of the best video games to date and has “the best” soundtrack ever.
“Where are you Marshall?” 
I was playing with an Harp and the Dorian scale just yesterday on my keyboard, and suddenly, it hit me!
http://www.youtube.com/watch?feature=player_detailpage&v=ehZMQ9Q1Jko#t=1637s