have you considered looking at
www.hotwire.com and (also available at .co.uk, but remember those prices are in GB£) ?
I've used both in the past and gotten good hotels, basically you are booking a room without knowing which hotel is will be until you're confirmed.
Hotwire give you a basic description and set rate, ie 3* midtown east, with x /y /z facilities and price is $125 per night. When you book you are given the hotel name, last time I went to NY we got Millenium UN plaza for $127 a night, compared with $219 listed price.
Priceline ask you to place a bid, so you go in and ask for the area, the hotel rating and the price you are prepared to pay, if a hotel is prepared to accept that price you get the room, (in Brussels we got a 4* for Eu48 compared with listed price of Eu129).
www.betterbidding.com give you a good idea of bidding strategies and a lot of hotels are identified. If you haven't used either of the sites above, I'd recommend really checking out this site, and what sort of prices people have paid for similar period.
The major downside of both of these sites is that once confirmed they are non-refundable....
I'm currently checking them out for a Jan'07 trip, but I've also got my eye on the Crown Plaza at the UN, its showing good rates (non refundable) from about $140 a night! Its a reasonable location, and have pretty good feedback on tripadvisor.