What Sith Lords were turned to the Light Side?

I have heard of a ton of Jedi that have turned to the Dark Side and became a Sith. (Exar Kun, Darth Malak) I've even heard of a few Jedi that have turned to the Dark Side and then found their way back to the Light. (Revan, Anakin, Qel-Droma) But I cannot seem to recall any Sith who turned to the Light Side. I think I might have read of one, but I cannot remember the name or story.

Are there any Sith that have turned to the Light? Hell, have there even been any Sith that have turned to the Light Side and then returned to the shadows of the Dark Side