Airbnb has a sign up bonus and all you need to do to get it is to use a referral link when you open your account.
The Genius program by Booking gives you 10 to 15% extra discount on prices that other customers won't get.
The reward system by Hotels gives you 1 free night for every 10 nights you book.
Save 10% or more with member prices and collect points which you can redeem for even cheaper stays.
Agoda with its reward system Agoda Cash could give you between 4% and 7% back on your reservations.