Jon Irenicus - David Warner (why anyone else?)
Bodhi - Christina Ricci
Minsc - Ralf Moeller (the big German actor who played Conan on TV)
Edwin - Alan Rickman (comical as well as evil)
Jaheira - Michelle Pfeiffer
Valygar - Will Smith (just to spice up the role)
Viconia - Catherine Zeta-Jones
Nalia - Drew Barrymore
Keldorn - Sean Connery
Saemon Havarian - Ewan McGregor
Cernd - Toby Maguire
I'll post more if I can think of any.
The thing to remember about the main character and Imoen is that they're only supposed to be about twenty-one years old, so I think we need to avoid picking thirty-five-year-old actors for those parts (no offense to fine actors such as Cuba Gooding, Jr.). The other characters might be a little (or sometimes a lot) older.