Oddly enough - game and movie soundtracks. Mostly game though, because it's music designed to be ignored.
I knew a coder who listened to the Muppets Christmas Sing-Along on repeat for about 10 hours during a marathon coding session. At about hour 9 she started to feel like she had lost her mind.
Edit: I just listened to Zero 7 on pandora, and it's awesome. I think I've found a new favorite.
About game soundtracks: they're also designed to be catchy given very constrained sequencing. On, say, the PS3 or the Wii, you can just have a full, ambient MP3 and nobody will bat an eyelash. But on, say, the NES, you had to make every tone count, just like you had to make every pixel count. This pushed games composers to focus on the core melody, giving the world such memorable tunes as Mario and Zelda (Tetris was just a conversion of a real song, interestingly.)
Of course, after these well-thought-out melodies are born, they can be dressed up all you like. http://ocremix.org/ is the exemplar there.
I knew a coder who listened to the Muppets Christmas Sing-Along on repeat for about 10 hours during a marathon coding session. At about hour 9 she started to feel like she had lost her mind.
Edit: I just listened to Zero 7 on pandora, and it's awesome. I think I've found a new favorite.