are both sites that list vacation homes and condos for rent by owner. We have found some surprisingly good deals, especially when travelling with family (kids, in-laws, etc.). You can frequently rent a nice house in your desired location for less than a hotel room.
Where are you? Some places are dirt cheap to go to from the East Coast, but a fortune from the West (and vice versa).
If you are inclined to do a cross country trip, I have always wanted to try a one-way RV rental from www.cruiseamerica.com
They are using these one-way deals to reposition some of their "fleet", so they make it really cheap.
I also cruise the "deals" section of www.frommers.com
Sometimes you will find a great sale on a destination you never heard of. That;s how we ended up going to Malta for cheap a few years ago (5 star hotels for $50 a night, etc.).