Also, I'd be very careful about being sure one knows what one wants to work on. It may seem like that now, but a lot of people do a lot of bouncing around in grad school, keep an open mind, and remember that almost everyone drifts a little bit in their area of specialty. Having an advisor who doesn't do exactly what you want to, even if you do your thesis on their kind of stuff, doesn't mean you'll have to do that forever.