Can be from any game, and any type of song. As long as it's your favorite.

Mind is World of Warcraft: Night Song.

http://www.youtube.com/watch?v=Z9iqUVY15VI

http://www.youtube.com/watch?v=MkWWx0YSyM0

http://www.youtube.com/watch?v=zqqq8uqSDnk

http://www.youtube.com/watch?v=sT9ReWDV0IU


First time I played this game I must have been around 5 years old on my super nintendo. It was such a huge difference from Donkey Kong Country and mario.
This song and all of it's many renditions is just so poignant, nostalgic and amazing.

Mech Warrior 2: 31st Century Combat had the best game soundtrack of all time. Every song was great but this was one of my favorites.

http://www.youtube.com/watch?v=2Fil6W5KGVA

The best part was those are the songs you got to play your missions to. Felt so pumped going into a mission like that as my mech is powering up and running through the check list while that song kicks on in the background.

I can play this version of the Skyrim theme on piano...
http://www.youtube.com/watch?v=gdX2eY79CGc


...but I also can play/like Song of Storms and the Dire Dire Docks Mario song.

My favorite music genre is Video Game.

I have too many favorites to list.. I'm jamming to this at the moment though :3

http://www.youtube.com/watch?v=3kOjXM0sH84

Final Fantasy 7 Dirge of Cerberus
http://www.youtube.com/watch?v=ZPmx7Igan3o

I think this is the first Final Fantasy game I played and actually enjoyed (By enjoying it meaning I played Tactics before hand and didn't enjoy it much).

http://www.youtube.com/watch?v=mnO82Snh3y4

probably any Clannad melody, or the Angel Beats starter song.