I'm in a rabid posting mood today, so I figure I'll inundate my flist with a dose of my shameless plugs.
First, if you haven't friended my community, hphumor, definitely stop by and check it out. HPhumor is essentially a forum where fifty hand-picked hilarious writers and artists post their new creations. So if you like my writing, you'll probably like the work of the writers and artists that I invited to post at HPhumor as well.
Second, you should also go visit slytherin_sluts and hpvamp because, well, I just adore those communities and I'm in a shameless plugging mood. :D
With respect to fanfiction, you have to read:
Estate of Sirius Black v. Ministry of Magic
They are all HILARIOUS fics that I have read and highly recommend.
Finally, check out Reddiej's new fic community, reddiefix, and Fiendling's new art community fiendart.