Nikon D40 would be my suggestion for that price range (its MSRP is $599 USD). I have one (bought the kit that comes with the 18-55mm lense, plus got the 70-300mm as well), and its a very nice camera. Takes nice shots, very easy to handle and well reviewed.
We had a
similar thread going over in the Canada area, theres a bunch of links to review sites you may also want to check out as well.