I wonder why Mark Hamill never did any voice work for the new trilogy? That would have been cool and classy. There were certainly enough voice parts, and Mark is an accomplished voice actor, cartoon work being the main focus of his career for the past few years. Heck, even Warwick Davis got to be in Episode I- not that that is something Mark is necessarily envious of.
Maybe he has a surprise guest appearance as a wookie in Episode III and they are keeping it tightly under wraps.