1.) Korriban: I feel that, especially with the existence of the One Sith, Korriban should be a planet full of Rp! And tombs.....and terentatek's and other such....horrible things.
2.) Ziost: The Sith bastion home world after they fled Korriban. Every piece of lore says that there is a LOT of things still hidden there and that it is concentrated Dark Side much like Korriban were a planet capable of taking Force Steroids....