I absolutely love video game music, have a big collection of it and I listen to it all the time.
Here's a small list of games/series with music I love.
Metroid
Zelda, Majora's Mask in particular
Mass Effect
Warcraft
Portal

Not only do I love the originals of these songs, but all of the remixes of them too.
There nothing like some Metroid Metal to put me in a good mood.