Rental rates in our DC metro region tend to be out of orbit.
The Washington Post has a rentals search site:http://www.washingtonpost.com/rentals/
If you're interested in renting a condo (national search engine that lets you "drill down" locally)http://www.condo.com/
Craig's List is worth trying, and friends of mine have found good rental rooms that way in the region. I'd preach some common sense caution so you don't meet Jack the Ripper alone at night in the last house on the left.