Definitely Clive Owen...
As long as it's a British actor, as opposed to some of the names bandied about a few months ago (Eric Bana?? Hugh Jackman?? I think even Russell Crowe was mentioned!!)
Have to disagree with Pjm, having read the books as well as seen all 20 of the official films (we'll draw a veil over Never Say Never Again), the nearest actor to the written Bond was Timothy Dalton. He had the edge and look that made you believe he really could be a cold hard agent & killer...