If I don't have my heart set on a particular hotel, then I like priceline.com a lot. I check biddingfortravel.com and betterbidding.com to see which hotels people have been getting and for how much. Use the free rebids by adding areas that don't have the star level you want.
The last time I needed a specific hotel, travelocity.com had the best deal with a 15% off coupon they seem to periodically offer via e-mail.