HotelTonight
You're finally about to meet the long-distance girlfriend or boyfriend you met on that dating site. And on the very slight chance that the address that was supposed to be your destination after three hours on a train doesn't exist in real life, you'll need a hotel and quick. (Or maybe you've made a last-minute sightseeing detour on a vacation and didn't book ahead.)
Either way, HotelTonight serves up same-day hotel deals in several cities. The hook is that only three hotels in each city are made available each day. They're categorized by low, medium and high price ranges. Discounts can reach upwards of 70%, and the deals are hand-picked by HotelTonight staffers.
Download links: iPhone
See also: Hotels.com, Kayak, Booking.com, HotelPal, Airbnb