I recently got a comment on the Alexis Bledel & Robin Tunney post that suggested this pairing, and boy, is it exactly right. Stanley Tucci and Mark Strong look so much alike, I spent most of Sherlock Holmes trying to figure out exactly whom to hate. Although Tucci and Strong typically play nice guys and mean guys respectively, they have a very similar aura. It's like they're made of the same DNA and one guy grew up in a supportive environment whereas the other grew up in a mob-owned dumpster.
I also think Mark Strong looks exactly like Andy Garcia. Oddly I don't see any such resemblance between Tucci and Garcia.