Sometimes I listen to metal (my default favorite genre) and sometimes I prefer various forms of electronic music: techno, house, trance, EDM, etc. Other times I go with classical: Dvorak, Wagner, Bach, Fauré, Handel, Vivaldi, Philip Glass, Carl Orff, etc.

But a lot of times what I actually prefer is to put on a movie, one that I've seen like 100 times, so that I know it so well that I don't really get drawn into the story and lose focus. I'll turn the volume down moderately low, enough to be audible but not overly distracting, and play The Matrix, Hackers, Antitrust, Sneakers, War Games, Tron:Legacy, Rad, The Social Network, Inception, or something like that and let that serve as my background noise.