I think Jude Law would play a good young Palpatine. Either pre-PT territory or the dreaded Emperor Clones.
I also was thinking that Tim Dalton:
Could make a good Karrde...
but he's probably too old so I'll say he'd make a great Garm Bel Iblis.
And This guy (whoever he is?):
Would make a great Anakin Force Ghost if they ever decide to tinker around with the canon ending of Return of the Jedi.