Stuart Townsend, Joseph Fiennes and Naomi Watts in Harry Potter and the Half-Blood Prince? Now given there’s not a single legitimate source involved yet it’s far from certain, but folks are speculating Watts for Narcissa Malfoy, Fiennes for Tom Riddle Senior (ha ha!) and several parts for Townsend, most of which he seems to be too young for. (Rufus Scrimgeour? Fenrir Greyback?)
Warning: Don’t expect the comments at the link to be spoiler-free for Deathly Hallows.