IN NO PARTICULAR ORDER:
Tom Hardy- The man is a great actor. He recently played Bane in The Dark Knight Rises, and had a critically acclaimed preformance. Lets see how he can do with a regular voice and a full face.
Bradley Cooper- He was rumored for a role in Man of Steel as Mr. Lex Luthor, who is, as he would put it, "The greatest criminal mind of our time". Craig vs Cooper could be an okay fight, with the only setback being the age difference.
Kevin Spacey- Speaking of Lex Luthor... Spacey has been denied his chance to be in Skyfall, but that isn't to say "Mr. Spacey won't return". He is age appropriate to play a villain such as Emilio Largo or Ernst Stravo Blofeld.
Rhys Ifans- Again, a recent comic book villain actor. But the Welsh actor did a good job. Plus, he's almost the same age as Daniel Craig. He can possibly be a good runner up for Javier Bardem.
Idris Elba- We need a black Bond villain, not a black Bond. The man is big, and as the rest of the men on this list, a great actor. A villain you may recognize him as is as Roque in the movie The Losers.