Surely, in the very near future, we are going to see The Valeyard reappear in Doctor Who, almost 30 years after his most telling appearances during The Trial Of The Time Lord? Thanks to "The Ultimate Foe" and a helpful description by The Master, we know that the Valeyard is "an amalgam of the Doctor's darker side, somewhere between his twelfth and thirteenth incarnations," which would suggest that once Peter Capaldi moves on (hopefully not too quickly,) the thirteenth reincarnation will be The Valeyard. But then again, that "between" suggests that there's going to be some overlap. We of course have hints that the Valeyard is due to reappear - thanks to"The Name of the Doctor", in which the Great Intelligence tantalisingly stated that "Valeyard" is one of the names by which the Doctor will be known before the end of his life. So why not sooner, rather than later? If Peter Capaldi is indeed set to play the twelfth doctor (and not the thirteenth as some theories suggest,) we're closing in on the point in the canon that The Valeyard will come into existence. His time is now, so it is becoming prudent to suggest who could be playing the villain. If there's one thing Hollywood's fascination with British Machiavellian villains has proved - particularly during the action movie heyday - it's that we have a plethora of actors on our shores who are particularly suited to icy malignance, and thus we have a long list of available options for The Valeyard. Despite Capaldi's former associations with both Doctor Who and Torchwood, we've limited the options to those actors who haven't yet appeared in the show, to maximise impact.
Honourable Mention
Peter Capaldi The chances of it actually happening are probably very slim, but there is something irresistible in the idea of Peter Capaldi playing his own villain opposite himself, or at least the writers pulling a major switch on the audience by setting up Capaldi as a good Doctor, but then revealing him as a villain (perhaps to John Hurt's Doctor?) would be great. Capaldi has proven over his illustrious career that he is far from averse to playing villainous characters, and in Malcolm Tucker in particular he has considerable mileage playing a scheming, hyper-intelligent Machiavellian figure (it is perhaps wrong to call Tucker an outright villain.)