[quote=Griever]
One-Winged Angelsry
[/quote]

What? I think that's a legit choice.
[quote=Dervish]
Doneky Kong
[/quote]
After years of repressing it, that song comes back to get stuck in my head.

And now to dominate the thread.
First off, is the song that introduced me to the genre. You see, I used to be one of those die hard Nintendo fanboys, and I thought anything that had to do with the X-Box was trash. Until a faithful day while I was at a Boy Scout Camp, in the Music merit-badge class. The instructor played a simple tune on the keyboard, a beautiful tune. Then he added in the chants, and my heart melted.
[youtube]Z5yVOFokLVY[/youtube]

This next song comes from my favorite video game of all time. It's not a very popular game, but it was immerse beyond it's time. And for a pre-teen with very little friends, I became enveloped in the lonely world of Tallon IV
[youtube]LudFV61zsaw[/youtube]

Another entity from my Nintendo days is Star Fox. This is the game that got me into Sci Fi, and into gaming. That may make me a bit biased, but I did always love the wild-west bandit theme I got from this song.
[youtube]4X_7bdD8P0w[/youtube]

I'm also obliged to post this game. I generally find the Final Fantasy series to be grossly over-rated, but there was always one that stood out to me, and the score attached with it remains my favorite retro OST.
[youtube]N1QgLqWb0rE[/youtube]

This next song was one I discovered in possibly the darkest period of my life, literally inches from suicide. That may sound a bit dramatic, and I don't know why, but this song clicked with me somehow. Becoming my personal theme:
[youtube]oH0v1tCYhZI[/youtube]

One of my favorite overall OSTs for a game is the Gears of War series despite having never played any of the games.
[youtube]rxgTlQLm4Xg[/youtube]

Another theme I love from a game I have never played:
[youtube]FoT5qK6hpbw[/youtube]

Of course, the game I have dedicated more hours to than actual human interaction also deserves a mention.
[youtube]VBPwCmU0V-Q[/youtube]
 
I literally have entire entire libraries for this.