Marcel the Monkey from Friends hasn't gotten much work lately. But he would only fit the part if they decided to go for a more comedic feel.
Personally, I'm rooting for the Indian monkey from Outbreak. We know he can convey tragedy and quiet, struggling nobility of purpose. Just look at that face!
If they decide to do an animated version (Pixar, I'm looking right at you), they could use this New York Times cartoon as a body model. He's a natural showman! As for his voice, I dunno, what's Kevin Spacey up to these days?
I was going to suggest that if Peter Jackson's King Kong is a hit, they could use the ape from that movie to play monkey-Scopes. But since there don't seem to be any pictures of the KK ape online yet, all a Google image search yielded was shots of Jackson himself. However, it occurs to me he wouldn't be a bad choice by any means, having as he does a sort of fat stoner orangutan look going on.
How about this dame whose socks have been rocked by Orlando Bloom? She's not a monkey either, but I found her picture while I was looking for shots of Marcel, and I think she's a natural. Plus, today, about a million public school teachers in Tennessee look like this.