for me, something familiar. set on repeat. the primary point is not the music, it is drowning out conversations my co-workers are having. Otherwise I become that irritating guy who jumps into every conversation within twenty feet of his cube. white noise doesn't work as well... the simple patterns in music, I think, help a lot.
At a secondary level, some music seems to act a little like stimulants. But that is secondary to drowning out conversations.