Online travel agents make commissions of approximately 15% to 25% of the price of the accommodation booked. Some share that commission with travellers through loyalty programs. Others give discounts upfront, or share some of the commission with "affiliates" who refer other customers. One such service is JetSetter, who has discount quality accommodation, and shares 5% with the guest and 5% with the referring affiliate. See Jetsetter. (I use this service by the way, and it is good. I have stayed in luxury accommodation at great prices.)
Another good referral program is OFX (OzForex) which is an international wire money transfer business. It is in competition with Western Union, and is much better value. See OFX website.