Use www.priceline.com in conjunction with www.biddingfortravel.com .
Scour biddingfortravel.com first. Try to stay clear of the owner who has a personality that could curdle milk. Then you will know what $$ amount to bid on Priceline.
I have to second Tozz's recommendation of these two sites used together. After you have had success with this strategy its unlikely you will ever pay full price again for lodging unless its an area not served well by priceline.com
We just returned from our third year of travel to the southwest, staying in $150-$250 hotels, and never paying
more than $75 a night. You can figure on paying about 1/3
of the lowest advertised rate. In our case the range was
$55-$75 a night, for very decent places.
But, like with frequent flier miles, you have to be a little flexible about when you travel, and deal with some
uncertainty about where you might stay within a geographic region. If you have ever used priceline, you will know what I mean.
Often for a few dollars more than the "motel 6", you can
upgrade to Hyatts and Omni hotels.