Gather is my favorite site, but I do use Superpoints, Amazon, and Ebay almost as much. Each of these sites are fun for me. Ebay I use for my collections and hobbies, so I try to stay off that one as much.
I find my coin collection is rather expensive and addictive. Maybe someday it will pay off, but so far it has done nothing but cost me. I like sites that give back. What are you into? How's Facebook?