ben_danger said:

well, maybe he should have LESS dignity. he was supposed to be this big-bad in ROTS, a jedi-killer who would be a real threat to obi-wan later on. yet all that is said of him by the jedi is that he is a coward, and they just send ONE guy to fight him.

giving him a higher raspy voice, and really playing on how greasy he is could strengthen his character alot more. when he suddenly reveals that he can fight later on, it could be a bit of a 'bummer we underestimated him' moment. certain elements would need changing to achieve this, but its worth a thought.

i tried this voice change AGES ago - http://www.youtube.com/watch?v=znm5AllHbG0

That's where the Cobra Commander voice could work out really well. It's raspy and menacing, but not in the way Vader's is. And it works with the whole "Griveous is a coward." angle.