^ I think he'll probably have a British accent.
Leonard Nimoy is down on the cast list on IMDB as "rumored" to voice Smaug, but I don't know where that comes from. I've never seen a news story or anything saying they were considering him.
Hm, what about Christopher Plummer? His voice isn't deep and booming like Christopher Lee's, but it has gotten a nice gravelly quality since he's gotten older, and The Hobbit is the sort of fantastical thing he's liable to do. I could see them casting him.