slytherin100 -- a weekly challenge drabble community focusing on Slytherin characters.
lazysundaydrabs -- The aim of Lazy Lie-In Sundays is to offer up a weekly dish of feel good, Harry Potter drabbles (no romance required).
hp_nextgen100 -- A drabble community focusing on the next generation of Harry Potter.
of_the_moon100 -- A multi-fandom drabble challenge community with a focus on het pairings.
slashthedrabble -- A multi-fandom, slash-oriented drabble challenge community.
crossgendrabble -- A weekly drabble contest featuring cross generation pairings.
obviouslysnape -- For discussions of Severus Snape and posting Snape fanfiction and fanart.
everyfandomfest -- A fanfiction fest for any/all fandoms of all types
To fernwithy for the idea.
To HP100 for the general premise and probably more borrowing from the rules than I realize.