Both have great databases for hotel content, but I'm not sure of what restrictions they have for their API.
P.S. I also know Wego (http://wego.com) have an API in the works, if you can get in touch with them through their contact form they can probably work something out (Disclaimer: I used to work at wego.com)
HotelsCombined thinks they can get away with charging $2000 for API access. Kayak doesn't provide much functionality. Wego looks great. Know anyone that I could contact their to get access too today?
Both have great databases for hotel content, but I'm not sure of what restrictions they have for their API.
P.S. I also know Wego (http://wego.com) have an API in the works, if you can get in touch with them through their contact form they can probably work something out (Disclaimer: I used to work at wego.com)