http://ink.accio.nu/
A fanfiction archive for any stories featuring a member of a dark family (as well as dark characters/ghosts/Slytherin et cetera). All ratings; moderated. Fics do not have to be dark in nature.

http://www.portkey.org/
An archive that hosts fanfiction and artwork for the ships of Harry/Hermione, Lily/James, Draco/Ginny and Ron/Luna.

http://www.restrictedsection.org/
An archive strictly devoted to the adult Potterfic. All fanfiction is NC-17 rated.

http://dark-methods.net/er/
A Draco and Luna fanfiction archive and community

http://www.coffee-and-chocolate.com/
A Fan Fiction Recs site, with a focus on general and canon-friendly fiction. Regularly updated.