GeekDrop officially has a Sith guild for Star Wars: The Old Republic. The guild name is "Vile". Muahahahahaha!
Feel free to apply! Clicky
Update: GeekDrop now hosts the Vile guild forum right here on Geekdrop.com! If you're interested in applying to Vile, please either contact Stardogg, Gore, or Bourne in-game on the Sword of Ajunta Pall server.