LOL, Alan CUMMING? I've met him and he's all of 5'2 and was playing with a Barbie Doll. I kid you not. He is the LAST person on the planet who would be a good Voldemort, I'd be laughing too hard to take any of it seriously.
Rent Red Dragon. Then come back and say Fiennes would be a bad Voldemort.
And for those who think Voldemort is not supposed to be attractive, Tom Riddle was attractive. Besides, with proper makeup, this will not be any sort of problem anyway. Its all in the eyes, and Fiennes has the coldest eyes of any actor I can think of.
Perfect choice.