For Fallout and Oblivion, I used to use Fallout Nexus and The Elder Scrolls Nexus. They worked alright, but most of the mods where crap and a couple of them had viruses attached that were a pain in the ass to deal with. With Skyrim, Bethesda is going to share mods through the Steam community, and I think it's a great idea. So where are you going to get yours?