Have you watched/read Detective Conan/Magic Kaito?
s2lou is arguably one of my favorite fanfic writers PERIOD, and of them I especially recommend
Spandex, Seven Possible Uses Of,
Of Moving Castles (DC/MK in Howl's Moving Castle AU), and
A question of Pride and (which is incomplete and probably never to be updated, but still worth the read). Also
Gems' Entry (a compilation fic) has a bunch of great chapters, of which I'd ESPECIALly recommend chapter 9. So. Good.
If you've ever watched/read Gakuen Alice and never tried fanfiction, you missed out!! b/c
Meocaroba has some GREAT FICS such as
you've got the morning (i've got midnight) (I LOVE THIS ONE SM) and
knives, fights and strawberry ice cream,
i don't want to die (but i quite like heaven), and
to have and to hold (these three are in the same universe, I believe).
HYOUKA: yes, that beautiful anime/ln that features oreki houtarou.
thundercow is also one of my favorite writers, and you'll probably see why once you read
There Are Questions I Can't Answer,
The Rain is Trying to Tell me Something, and
Oh Suzume (this is apparently kind of a crossover-ish fic with Pacific Rim, which I still have no idea is about but is sooo goood regardless). thundercow also has a bunch of other fandom fics, so scroll through and look for any you know and read'em. hehehe.
Fairy Tail: I remember that I thought
808Lionfire had some great fics, but I haven't read them recently enough to remember except for
Seven Attempts to Fall. Hahaha.
Honorable Mentions:
An Outsider's Perspective (Kimi ni Todoke fanfiction, the only one I found to be actually good so far),
survival rate (Lovely Complex fanfiction-- again, the only one I found to be good in its fandom so far),
sealed in wax (Pride and Prejudic fanfiction that always puts a smile on my face),
The Beauty of Beast Boy (Teen Titans fanfiction that I read every year),
Numbers in Choreography (another Gakuen Alice fic, with OCD-ish Natsume), and
Kokoroyomi Monogatari (yet another GA fic, lol, but I found it funny).