Super Metroid, and Metroid - Helps me get a basis on how to write darker music, the feel inspires me in different ways over and over again.
Tropico 3/4 - Upbeat and really influences how I make my town I noticed, when I mute and play other music my town seems to differ entirely.
Singularity - Seriously this music creeps me out all the time.
Grand Theft Auto: Vice City / Grand Theft Auto: San Andreas - Really puts me into the game, old school tracks to give the authenticity of being at that very time and place.
There's more, but can't be arsed to write the rest down.