Have you read the wirecutter tripod roundup?
http://m.thewirecutter.com/reviews/best-tripod/
Don't cheap out on a tripod. For most photographers, you'll really want a ball head and something that's going to be sturdy and easy to maneuver. Make sure you get some kind of quick release plate that you'll be comfortable just leaving on the camera body as it makes using the tripod much easier.
Also, try to buy a size tripod that you can use comfortably without extending the center column too far (or at all) since that tends to compromise stability.
That said, I don't agree with Thom Hogan that you should just buy the top of the line to start with. Many enthusiast photographers buy a tripod, then find it too cumbersome to use frequently.