I have a canon 20d and its awsome. I would would concider Canon and Nikon for making DSLR since they are pimp camera companies and have great lenses. The Canon XT(350D) is a nice camera with a lot of the same features as the 20D. However it is a bit smaller and feels funny to me. But i'm used to bigger camera Bodies so i'm biased. If you are on a budget, the Canon digital rebel(300D) is dropping in price pretty quick and would be a easy way to get a cheap body and spend more money on lenses) Also Check out the Canon 10D. Its a great camera and is pretty durable. It was replaced by the 20D and also dropping in price.
Nikon makes some good DSLR cameras as well. I have used the D70 and found it to be one of the most comforatable camera in my hands. However, the features are not up to par with Canon and the prices are a little higher. However, it is a good option if you have nikon glass(lenses).
One thing to concider is the lens options. You will be spendy most of your money on lenses since they can be used on the newer models in that camera company bodies. For example. The Canon EOS lenses will work with all the new bodies for a long time. This have been around for long time and are expected to be around for a great deal more. I have gone through a couple bodies but still use the same lenses.
Canon Rebel XT (350D)
Canon Rebel (300D)
Hope that helps a little. PM me if you have any other questions.