You'll notice that the Stargate list is the longest. I tend to be a one-fandom-at-a-time sort of girl, and Stargate's my current media crush. But since a number of my favorite Stargate authors write in other fandoms, I am occasionally lured across the fence to wander in other pastures.
And while I've often said that most fanfic falls under the auspices of Sturgeon's Law, there really is some damn good writing in fandom. The pieces listed on this site are, in my not terribly humble opinion, some of the best, or most inventive, or just plain fun writing that I've found in these fandoms.