Winona Ryder in anything. Especially Bram Stoker's Dracula and Alien Resurrection. And that's just two. I could go on
Clive Owen in anything. He's just so wooden! And he can't do accents
Kate Beckinsale in just about anything, but especially in The Aviator. Scarily she was quite good in Much Ado About Nothing.
I was also going to say Halle Berry in Monsters Ball, but then I just thought, "no, in everything". She makes me cringe. I don't think she can act at all.
Then there's Ewan McGregor and Samuel L. Jackson in the last three Star Wars movies.
Keanu Reeves is another. Was terrible in Bram Stoker's Dracula - double whammy! Keanu AND Wynona in the one movie!

And in Much Ado About Nothing. And a lot more.
On and there's Bill Nighy who's just the same in everything. All Bill Nighy-like and seemingly unable to act a part or character. He kind of ruined Underworld for me, once I'd got past hating Kate Beckinsale. And I wasn't keen on his character in Enduring Love and I'd rather he hadn't been in The Constant Gardener which is one of the best films of all time. I can ignore him in it though as he plays a ****
