If only Orson Welles were somehow still alive.
I love Alan Rickman but I know I'd just be cracking up. Isaacs is too sniveling in the Potter movies at least...I don't remember him well enough from other roles to really comment though.
Liam Neeson can't because he's the Jesus-Lion.
Sean Connery already got to be dragon.
Patrick Stewart...yeah, I'd also be cracking up. I love his voice (who doesn't?) but...
As long as Jeremy Irons can be less of a fruitcake than he was as Scar...no, still, not feeling it. Too weak.
Christopher Lee would be a safe choice, but regardless might not agree to it anyway.
That is such a horrible list from ToRN, though...no offense. Seems mostly like a joke list...I mean, Morgan Freeman? Hmm...actually I bet Mark Hamill could pull off a pretty good Smaug voice, haha.
So, a couple more hilarious Smaug ideas:
Peter Ustinov. O.m.g. So terribly terribly hilarious (though also dead

).
Also,
CaptainofDespair just suggested they just get Christian Bale to do his *Batman voice*...much lolz.