Personally, I would stick to Nikon or Canon, as they are the two "heavy weights" in the DSLR space.
I am not familiar with Canon, so I will stick to the Nikons - depending on how comfortable you are with DSLRs, you can go D3000 or D5000 - D3000 is the entry level model and the D5000 is a little bit more advanced. Read the reviews on dpreview.com/bythom.com/stevesdigicam.com to get a sense of pros/cons. From what I have read, both are good beginner cameras
If you want to go brand new, take a look at the Camera Store (
www.thecamerastore.com) - they have a D3000 + kit lens for just under $500, a D5000 + kit lens for $650 and a D3000 + 2 lenses for just under $700. If you're just starting, any of these combinations will keep you learning for a while (and the kit lenses are decent lenses). If you are more experienced, pickup a D3000/D5000 body and get a 50 f1.8 or 35 f1.8 and that will keep you in your budget range as well.
The other option, as someone mentioned, is to look at "pre-owned" - kijiji or craigslist have a lot of people selling their cameras/lenses
Good luck...if you have any questions, feel free to ask