I'll start off with Raiden II's Repeated Tragedy.
A local restaurant had this game, and every time we went, I'd beg my parents for money so that I could play it. I wasn't very good at the game, so I never got past the first stage, and so I heard this song a lot. Really gives me nostalgia.
Also got to shout out Streets, from Timesplitters too. I put a lot of time into this game as a kid, and this song is what got me into futurepop (love me some VNV Nation).
The ambient music from Mass Effect 2 that plays while you're probing for resources. I know lots of people hated that mini-game, but I found it extremely soothing and spent hours and hours doing it.
The galaxy map song from that game is what got me into ambient music and changed my life for the better. It just hits my brain perfectly