The Nikon 5700 is a great buy with 5 MPs and super sharp images. Its just over $1K at retail, but I've seen places on line selling it in the $800 range.
If you have to stick to a budge at $500, the Nikon 4300 is a great buy.
This site has lots of info and very comprehensive reviews. If you click on Galleries they have samples from all the cameras also.
http://www.dpreview.com