Firstly, I am so sorry if I get names wrong, it has been a while since I have read them and I only looked at the first 10 or so pages of this thread.
Personally, I'd have the following (cannot give all as I just cannot choose for some of them) on some conditions:
Belgarath - Jeremy Irons if he really went for it. He had good foundations in Eragon, and despite it being a bad movie, he was still good in it.
Durnik - Jim Caviezel with stubble and if he let himself go a bit.
Beldin - Andy Serkis. He can play "hidden" roles well.
Zakath - Sean Penn or Christian Bale or Keifer Sutherland
Poledra - Michelle Pfeiffer. She can wear that tawny hair, is the right age and that timeless beauty.
Queen Nyssa - Either
Olivia Wilde (Thirteen from House) or Monica Bellucci
Voice of the Orb/Good Prophecy - Rowan Atkinson
Adult Garion - Edward Norton (ok age-wise maybe not-so, but he does have that timeless hero look about him)
Adult Ce-Nedra - Natalie Portman (but that's all I've found)
Hettar - Christian Bale (if Sean Penn is Zakath) or David Boreanaz
Torak - Ron Perlman
That's all I have so far