I created a post a while back about actresses in negative roles. I'm doing the same with actors now. I am sure I left out some prominent ones, add them in the comments.
To start off - SRK. His characters had shades of gray in Darr, Baazigar, and Don to name a few. I personally LOVE him in negative roles compared to his romantic image. Don 2 is about to release and I can't wait. I also liked the promos of Don 2 better than Ra.One, but I guess to each her own.