This is a very simple post.
I have a small rickety tripod and while it's good enough for the odd picture it's pretty bad if there is even the slightest bit of a breeze. Pictures are soft and shaky and now that I've started to experiment with long exposure work the tripod is proving to be truely dreadful.
So a word of advice - you've got a DSLR with more mega-pixels than you can shake a stick at and probably several lenses and a bunch of other kit which you've paid a pretty penny for. So don't buy a cheap tripod. I'm now taking most of my pictures on the tripod so what's the point in having one that ruins every picture?
With tripods you definitely get what you pay for but there is an element of name brand price hikes e.g. Manfrotto and Giottos. However they do make bullet-proof stuff but if you're going to pay less than £60-70 you're going to be looking for a new one in a few months time. Once you're in the £150 range you should be safe for a while - remember you might need the head to go with it.
One other thing to note is that tripods are designed for a certain weight maximums and once you start buying top end cameras and large lenses the weight piles on. Keep that in mind if you've got ambitions of being more than a casual clicker.