For all you New Yorkers, or anyone who might need to rent a car in the city, this site is definitely worth checking out. I always rent from here and get much better rates than going directly through the rental agencies. I think they're mostly geared towards renting cars overseas, but you'll see links on their home page for "U S A - Alamo" and "U S A - National". I always go with Alamo because, in addition to the great rate, you also get a free tank of gas.

Only downside is that you have to put down 15% of the cost when you make your reservation, and depending on how far ahead of time you cancel your reservation you could lose all or part of it. In my mind though, the great rates make it worth it.