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

http://lumos.sycophanthex.com/
A general Harry Potter fanfiction archive

http://erosnsappho.sycophanthex.com/
An archive for slash and femme slash fanfiction from the HP fandom.

http://inkstain.inkquill.net/
A fanfiction archive containing same-sex relationships (slash)

http://www.fictionalley.org/
Huge fanfiction archive - all ships, all lengths, all the time!