ONE:NIGHT - Last minute reservations at only the best hotels
MakCorps - Hotel Price Comparison API
TripRebel - Book your hotel now & get a refund when the price drops
Gopher - Better hotel deals automatically, every time + cash back
Hotel Room Alerts - Snag a room at a sold out hotel
Sponstayneous - It's like Scott's Cheap flights, but for Airbnb's.