In order to find the best deals, it's better to check out several sites. I always do big research as all sites provide different offers. Here is a full list of such sites, just have a look travelsites.com/vacation-packages/
There are many websites on which you can buy such packages. Many depends on what exactly do you want, your budget, etc. For example if you want some exotic I can recommend these Top Rated Swinger Resorts, we have been in Temptation Resort in Mexico and it was very cool! Nature is very beautiful!