The Arca-Swiss B2 is the "ballhead" that's really a pan-tilt head with independent movements. Arca-Swiss balls are elliptical so that as the head tilts, the resistance increases, so the camera doesn't flop over, and the B2 uses two concentric balls, I believe, so that you can adjust tilt and yaw independently, just like on a pan-tilt head, and it's rated up to 150 lbs. Neat concept, hefty price tag (around $700).
I looked today at a Levelhead, which is a leveling platform with an Arca-Swiss type clamp (comes with one plate) that is attached to a tripod head for fine leveling, or might be usable as a head by itself, if you don't need much tilt. It's really nicely made, but also not cheap ($495 at Photo Gizzmo--which is not as bad as it sounds, if you consider that it comes with the clamp built in and a plate).