SUNSEEK20
RatesToGo has the same 20% off promo from time to time. Not all hotels will be 'participating', but usually a good selection are included. Best thing to do is to search for the city and dates in the left, enter 'SUNSEEK20' in the 'I have a promotional code' text box (under 'Aditional Options'), and search. You will be able to see which hotels the promo code has been applied to in the search results.
Always check other booking sites to compare prices of individual hotels. I've found that ratestogo.com is usually not the cheapest, but can end up being the cheapest after 20% off.