Author has written 1 story for Harry Potter.
I like a lot of anime, manga, books, and movies including a few where the fanfiction is lots better than the original/canon. For example: Harry Potter was great up until the fifth book came out and it turned into a steaming pile of crap IMHO. Ranma never really ended and got really repetitive, but it was great in the beginning and near the "end" of the manga. I won't even read/watch Naruto or Sailor Moon unless it's fanfiction, but for some reason I DO like the fanfic.
Harry Potter: Luna, Hermione, Moody, Tonks
Naruto: Naruko (if she's the original or a separate person), Hinata, Shino
Ranma : Ranko (if she's the original or a separate person), Konatsu, Kasumi, Ono (Tofu)
Sailor Moon: Hotaru, Michiru
Teen Titans: Raven, Starfire, Gizmo
Tenchi: Sasami, Ryo-Ohki, Yosho
If you see any Ranma x Hotaru (from Sailor Moon) pairings that are well-written, I'd love to see them so please drop me a PM.