Tripods are a key piece of any photographer's kit, and there are as many choices for tripods as there are lens systems for cameras. So how do you choose? Here's a primer on basic tripod types, available options and things to consider when buying.
Main Things to Consider
There's an expression: good, fast, cheap. Pick two. The same applies to tripods, but change the options to sturdy, lightweight, and cheap. If you want a lightweight, sturdy tripod, expect to pay a lot of money for it. If you want something inexpensive and lightweight, don't expect it to be very sturdy. So it becomes a balance, and the key is in understanding how you will be using your tripod.
There are two main kinds of heads - ball heads and pan heads. A ball head has a single knob and the head easily rotates around until you lock it into position. A pan head has a pan lock, tilt lock for up and down movement, and a third lock for arcing the camera side to side.
This is the simplest kind of tripod head. A single locking mechanism provides a full range of movement for your camera. If you tend to shoot quickly, or with moving subjects, this might be just the tripod head you need. The trade off is that you cannot easily do panning shots, such as with panoramas, and a simple tweak in the tilt will force you to re-frame the whole shot.
With pan heads, multiple locking knobs give you precision in your tripod work. You can lock down the tilt and still adjust the pan without having to re-frame the whole composition. These are very useful heads if you do a lot of tabletop or macro work. The different locks give you precision in your camera movement and allow you to pan easily for panoramic shots or even for use with small video cameras. The trade off is speed. With so many adjustment knobs, it can take longer to frame and lock down your shot than with a ball head. If you want to use your tripod for both still and video work, definitely choose a pan head, but make sure the connector on the quick release plate will work with both your still and video cameras.
Other Things to Consider
If you're very tall, make sure to purchase a tripod with a high maximum height. You don't want to be bending over every single time you use your tripod. Make sure the tripod you choose is rated for the weight of your camera and the heaviest lens. If you think you might upgrade to a heavier camera in the next 5 years, choose a tripod that will handle the extra weight. Finally, always choose a tripod with a quick-release plate. These allow you to quickly remove the camera form the tripod without a lot of fuss.