Depends a lot on what your going to be doing. Macro? Fast moving birds? Hiking long distances? ...
Just to take the hiking issue: heavy is good in a tripod if you don't have to lug it about much. Heavy adds to the stability which is why you want a tripod. Heavy is also cheaper.
A good read on tripod prices can be found at http://www.bythom.com/support.htm
Thom might be talking out of your price bracket, but the point about not going cheap is still right on. A good tripod will outlast several cameras and lenes, a bad one will just clutter your closet.