Voice of Smaug?

[Thinlómien]

I would prefer Smaug to have an evil, sneering and amused voice, and not any macho masculine stuff. A woman could do Smaug as well as a man - but surely not anyone with a girly voice or an overtly feminine one. Also, his voice should not be a distinctively old voice, for even though he is old, there is something very youthfully playful in him. British accent would be nice but not necessary - as long as Smaug doesn't have a very strong American accent!

I don't have any particular actors or actresses in mind because I'm terrible at remembering their voices. Of the suggestions this far, Geoffrey Rush, Jason Isaacs, Derek Jacobi and Kathleen Turner sound quite good, but none of them is exactly what I'd like to hear.