Generally, familiar music. I can't think of any other commonality beyond what stems from the fact that programming doesn't facilitate the ability to listen to new music.

I was going to say--oh, Debussy and Chopin. But why be a snob when I also listen to early Madonna music, and stuff too horrible to mention except anonymously:

http://www.youtube.com/watch?v=Dsi8ho1PgKM

http://www.youtube.com/watch?v=sI5LWwC-cE8