I like to listen to a mixture, depending on my mood. Usually soundtracks to strategy games like http://www.youtube.com/watch?v=86QcIBZXqT4&list=PLB0FB8CDED1962C54, or other types of games like http://www.youtube.com/watch?v=0cXsoRRYf5A&list=PL880D572DF1EA418B, http://www.youtube.com/watch?v=uLXZXt8-KX0&list=PLeIDCtrbfdx-BQMS2UNmUMji5jl33e9N8, or http://www.youtube.com/watch?v=1ZHzbaV98go. I also find the http://www.youtube.com/watch?v=T8UlVthaxtg&list=PL9u7rbRjJmqDVOaeVdB24dTctKryI3oT6 soundtrack particularly immersing. I also like a good acoustic guitar sesh.

What music do you listen to whilst modding?

Note:

Brian Eno's atmospheric music makes good background music to!

Edit: Added links to some of my favourites.

Usually nothing. If I'm doing more intensive work I'd rather not squander the music as passive background stuff because I prefer paying attention to what I listen to. If I'm just doing a lot of grunt work on mental autopilot I sometimes don't mind having something to listen to, since I can devote more attention to it.

Last night I was listening through Karnivool - Sound Awake while doing some dungeon level design.