I haven't written anything yet... usually, I get a half-page into something and then permanently forget about it. The longest fanfic I haven't finished is a couple pages long and is a Mary-Sued Self insertion parody between with hardcore POTC fangirls getting sucked into FFVII... Don't worry, I have since reconsidered the overall quality of the idea/implementation I used right before the girls got to Midgar. Also, I have realised that the same fangirls would probably have watched the unfortunately canonical fanfic that is Advent Children and already found targets for their obsession.
Fandoms I read and know enough about to possibly write for in the order I found them: Pokemon, Babylon 5, Final Fantasy VII, Pirates of the Caribbean
Fandoms I sort-of-know: Batman, Spiderman (mostly movieverse), Star Trek, Stargate SG-1, Star Wars, Buffy crossovers (don't ask), Lord of the Rings, Firefly, and... Harry Potter (even though I really DO NOT LIKE the books - I mean, really. No one could possibly be as utterly inhuman as the Dursleys without anyone noticing (I really hope...) and their very relationship with Harry feels like a plot device for unnecessary angst. Which really gets on my nerves every time I try to read anything related...)
My most recent fandom addition is Danny Phantom, which is incredibly random (as I dislike cartoons). Maddie Fenton is my favourite character, so she's now my icon.
Sneaky Maddie is sneaking. :)