This is one of the hardest thing to answer..
But I guess I will say one of following..
Darth Bane
Exar Kun
Darth Revan
Darth Nihilus
Darth Sidious
Only one there just come to mind right away when I think of the Siths
Kotor 1-2
Jedi Knight Academy
Jedi Knight Outcast
Star Wars Empire At War (think that what the stragy game thing was called)
Star Wars Battlefront 1-2
Star Wars Force Unleased
All I really rember atm, even though I feel like I left some out >.<