How about an expanded universe line devoted entirely to the Dark Jedi and Sith. It could be called "Lords of the Sith" or "LOTS" for short. Some of the figures that could be included are:

WAVE 1
Marka Ragnos
Exar Kun w/ double-bladed lightsaber
Darth Bane
Naga Sadow w/ Sith Sword & Amulet
Lord Simus w/ removable head & Transparent Case
Freedon Nadd

WAVE 2
Ludo Kressh
Aleema
Satal Keto
Ulic Qel-Droma
Xanatos
Kyp Durron

WAVE 3
Jerec
Joruus C'Baoth
Maw
Sariss
Gorc & Pic
Sedriss

WAVE 4
Soft Goods Cape Darth Vader w/ Removable hand & 2-piece mask
Lumiya w/ lightwhip
Soft Goods Slice Apart Darth Maul w/ Removable cloak & break apart lightsaber
Soft Goods Darth Sidious (Palpatine) w/ Removable cloak & force lightning
Soft Goods Darth Tyranus (Dooku) w/ 2 lightsabers & force lightning
Flint

OTHER
Beldorion the Hutt & Jedi Leia w/ two lightsabers (Beast-Pack)