I used the "name your own price" deal on Priceline. The way it works is you first pick the dates you want, then pick the minimum star level of the hotel you want, then select all of the neighborhoods where you're willing to stay, then place a bid. For Manhattan hotels I usually start bidding at $110. Priceline will ping every participating hotel in those neighborhood and see if any hotel will accpt your bid. If more than one accepts, Priceline will give you the one with the higher star rating. If no hotel accepts, you then go up by $5 or $10 dollars until a hotel accepts.

Note that you do this AFTER you've given your credit card info, and as soon as a hotel has accepted your bid, you've bought the room. But they screen and monitor their participating hotels very closely, and you will never be put in a dump. The hotels I've gotten from bidding on Priceline were far and beyond the best hotels I've ever stayed at in my life, and I could never have afforded them otherwise. The lovely Murray Hill suite we just stayed in for $132 a night is going for $559 over on Hotels.com.