Intelligence, general rather than academic, is an absolute must. Impeccable music taste is near essential but exceptions can be made.
Sense of humour, to be very cliche. But not a typical one, one that actually understands and doesn't get pissed off when someone makes jokes about something controversial or whatever.
Nice voice is preferred. I don't care how good you look, if you open your mouth and it sounds like cow shit, take a hike. I can't talk to you like that.
-AC