I agree with Roy's advice. It's well said.
But of all camera gear talk, tripods are probably my favorite subject

So, here's some of my brain-droppings based on my experience:
There are a lot of features to look at and consider. Some of them may not seem important now, but when you're out in the field you don't want to be fussing with some blasted leg locks or center column that just won't work like you need it to.
BrandI've had experience with Bogen/Manfrotto, Gitzo, and Giottos. All of those are brands seem to be quite good.
In general, price is directly related to quality (true with a lot of things, but not all

). My philosophy is to spend a bit more and get a quality product that will perform better and last longer.
When I started this camera thing, I used an old tripod I inherited from my grandfather. I took it to Big Bend. It was terrible to use and I broke a few things.... bad experience!
Leg SplayGet a tripod that has independent leg splay, i.e. the ability for each leg to rotate and lock at several angles between vertical and horizontal. Here's an example of one leg fully "splayed" out:

The leg splay is an awesome feature when setting your tripod up on uneven ground and/or in a tight place.
Go ShorterYou can get by with a shorter tripod (or using a weaker, i.e. lower capacity, tripod that's not fully extended) with a couple of accessories. An
anglefinder (also called an angled viewfinder) will generally allow you to use your camera about a foot lower than eye level. An anglefinder will also make your life easier when you want the camera at a very low angle. Instead of laying on the ground to see through the viewfinder, you just squat down and lower your head to the anglefinder.

A
L-bracket (used as part of a quick release system) also helps. Instead of rolling the camera over 90-degrees to go from horizontal to vertical shooting (which lowers the viewfinder considerably), you just rotate the camera body and re-clamp.
Center Column LockThe center column locking mechanism can be a source of problems. I've had two tripods in the past that used a set screw (a screw perpendicular to the column) to "bite" down on the column. This design never seems to hold the column securely enough.
A better design is the rotating collar and collet system:

Ball TypeShould you choose a ballhead over a pan/tilt-type, I would advise you to get one with a metal ball. My first ballhead (a Bogen/Manfrotto 488RC2) had a phenolic ball. It worked fine when I used a short lens, but when I loaded it down with a heavy telephoto lens, the head would never lock well enough. Maybe it was something else, but I think a metal ball is better.
Leg LockThere are generally two designs used for locking the leg sections: flip-levers or screw-down type clamps. I've used both and each type works well. The flip-lever style is probably the easiest to use, but with a little practice the screw-down type is nearly as easy to use.
Quick ReleaseAn absolute necessity! Definitely get a QR system.
Each manufacturer seams to have their own proprietary system. But at the higher end of things, there's the Arca-Swiss system. This particular system is well designed and there are butt-loads of different camera and lens plates available. Brands like Kirk, Really Right Stuff, Markins, Acratech, Wimberley, and Arca-Swiss all make clamps and plates that are interchangeable.
Example 1This is a Giottos 1140 set of legs with a Bogen/Manfrotto 488RC2 ballhead. I used this rig on my last overnight hike into the Chisos. It's very lightweight (about 3 pounds total).
The tripod legs are well suited for a small point-n-shoot type camera. My trick is that I don't extend the tripod all the way - only to about 3 feet at highest, and I use an anglefinder and L-bracket to make it work for me.
Example 2This is a Bogen/Manfrotto 3021BPRO set of legs with a Kirk BH-1 ballhead. The tripod legs have been modifed - I removed the center column completely and all the crap that went with it. Like I stated previously, the locking device (a perpendicular set screw) didn't work worth a fart. But the legs are damn nice and well built.
This is a heavy set-up (nearly 8 pounds) and is complete overkill

It's better suited for one of those giant lenses you see at sporting events, although I lack such a beast (just can't justify spending $5 - 7K for one lens

). But it's nice to have a rig that I could park a car on if I wanted. The wind won't knock this thing over and I can beat the bears off with it.

Example 3This is a Gitzo GT1530 set of legs with a Really Right Stuff BH40 ballhead. The legs are carbon fiber and pretty light. The whole deal weighs about 3.5 pounds, and I will gladly haul it with me on my next overnight hike.


Anyway, good luck in choosing the right tripod + head. And Jeff's right, getting a bit of hands-on time is really a good thing when it comes to tripods and heads. Definitely go check them out!