Sounds a bit of a stupid suggestion because he is getting rather old but I think Richard Briers might be right for the role, his voice suits Smaug's characteristics.
I also noticed on page 1 that Beren had said Christopher Lee would like to play the role (Don't know whether Beren shares the view) I think he would really suit Smaug but maybe he could talk with a slightly less serious tone in his voice as he did with Saruman (A bit off the subject but I think he really did suit that Saruman role well, and he probably could adapt a bit to play Smaug).
