I listen to different music depending on what I build.
When I built my cathedrals, I mostly listened to Bach's Organ works and gregorian chants.
When I build other old stuff, I like to listen to random classical music.
When I build modern stuff, I listen to rock and metal.
Whenever I listen to psychedelic stuff such as old Pink Floyd and Porcupine Tree, my builds turn out really weird. :S