If you can afford $640, then the Canon Rebel XTi would be a great choice, however it takes CF cards.
http://www.newegg.com/Product/Produc...82E16830120070
The Nikon D60 is a great camera from what I've read/heard, which uses an SD card and costs $630.
http://www.newegg.com/Product/Produc...82E16830113088
Or if you want something for under, there's the Olympus E-510 for around $585 I believe.