While building, I usually listen to up-beat, lyrical songs. Usually Country Music or the occassional 'Weird Al' binge. I like to sing along with the songs while I build, it helps calm me down while sorting through my unsorted bins (which I really need to buckle down and sort someday).
While online, either browsing the forum, doing MOC research on Brickshelf, or browsing Bricklink for all the stuff I can't afford, I usually listen to instrumental stuff, mainly game music. If I feel I need more inspiration to build medieval stuff, I listen to the music from Lords of the Realm II, the game from which I get the music for my online movies. May they never be angry with me for doing so.
Give a man a fire and he'll be warm for a day.
Set a man on fire and he'll be warm for the rest of his life.