Any entry level DSLR would be fine.
I have the Canon Rebel XT, the XTi is very popular though.
As for nikons I think that one is good, I'm not sure if thats the model or not, however one of Nikon's entry level DSLR's is missing an AF motor, which you most likely wouldn't like.
I would wait for Martin or Robs answer though, I really don't know much.
O and I know S**T about pentax but I'm sure Rob can promote that.