What is the best digital SLR camera for under $500?

I am looking for a Nikon or Canon digital SLR camera for under $500. I have had a Nikon Coolpix L20 for a couple years now and would like to upgrade to a camera with a view finder and manual controls. I'll be starting college soon and will be majoring in photography; so it's also important that the camera is widely functional, long-lasting, and will help me learn the trade the best. Thanks ahead of time for your suggestions!