Oh good gods, that is a difficult question.
The obvious answers have, of course, already been stated: Morgan Freeman, James Earl Jones, Sean Connery, Ian McKellen, Patrick Stewart, Leonard Nemoy, etc.
Going a bit off the beaten path, I'd say Kristoffer Tabori in character as HK-47, (Observation: The meat-bag noted that his 'sandwich' was dry. Suggestion: Perhaps he could ring out his arm and produce a glass of water with which to wash it down.) the cast of Whose Line Is It Anyway?, Kiefer Sutherland, Gary Oldman, William Shatner (As he... walked down the... street! he suddenly spotted....... his goal: the coffee. shop. where. he was to meet... his. friend?!..."), I believe Liam Neeson was mentioned but he deserves another, and finally Michael Caine.
I could go on, but I've gone and messed myself with enough words already.
EDIT: I FORGOT RON PERLMAN, PLEASE FORGIVE ME!