Use the SSD for the OS and any important programs and games. They will benefit from the speed boost an SSD has over a HDD.
Put your music, movies, documents, unimportant programs and games on the HDD.
Put only games that will benefit from the faster load times most, so games like Fallout and Skyrim that constantly load are best. By comparison something like BF3 wont really benefit because it only loads at the beginning of the level. With online play it will be more the internet speed that matters than drive speed.