There's a huge difference between a good tripod and a bad one - maybe even moreso than between a cheap lens and a high end one (for one thing, if the camera's not steady, what good is a better lens going to do?!).

The right tripod for you depends on a few things. Budget? How far will you carry it (backpacking, or a 50' walk from the car)? How tall are you (really, if you're 6'-1" like me it can be tiring to stoop over one not quite high enough). The equipment going on it is also a consideration - not always so much the camera as the lenses if they're long and heavy.

A good starting point that I always recommend (and used to own but it's kinda short for me) is a Bogen 3001 and 3025 head which is sold separately. It's a good compromise of all of the above points, and under $150 USD complete (probably much less than that).