As Martin has already mentioned, Benioff and Weiss have stated that all casting suggestions should be posted over at the Westeros forums. The producers have an account there and have promised to check the suggestions. With almost two months worth of suggestions accumulated, poster Smoldering Hound has begun running polls to find out the most popular candidates. He has since posted the results of the voting. Below is the full list of actors for the pilot, as voted on by the Westeros forum members.
A Game of Thrones, As cast by the Westeros Board. Don’t agree with it? Vote in the polls (all character names link to their respective Poll)!
Jeffrey Dean Morgan as Eddard Stark
Ben Barnes as Jon Snow
Peter Dinklage as Tyrion Lannister
Alexander Skarsgard as Jaime Lannister
Emily Browning as Daenerys Targaryen
Tricia Helfer as Cercei Lannister
Kelly MacDonald as Catelyn Stark
Jodelle Ferland as Arya Stark
Asa Butterfield as Bran Stark
Rory McCann as Robert Baratheon
Rachel Hurd-Wood as Sansa Stark
Avery Clark as Theon Greyjoy
Harry Eden as Robb Stark
Rupert Friend as Viserys Targaryen
Elias Koteas as Jorah Mormont
Jason Mamoa as Khal Drogo
Max Pirkis as Joffrey Baratheon
Ray Stevenson as Sandor “The Hound” Clegane
Bill Nighy as Grand Maester Pycelle
Vincent Regan as Ser Rodrik Cassel
Ian Holm as Maester Luwin
Michael Fassbender as Benjen Stark
Ian McNeice as Illyrio
Ryan Simpkins as Myrcella Baratheon
Will Poulter as Tommen Baratheon
Tom Hiddleston as Ser Waymar Royce
With Locals cast as Beth Cassel, Jeyne Pool, Septa Mordaine, Ser Boros Blount, Ser Meryn Trant, Jory Cassel, Harwin, Hullen, Will, and Gared
Winter Is Coming: Not a bad list. Certainly seems about right for the budget. There are a few actors that probably wouldn’t be cast due to scheduling conflicts (for example, Skarsgaard is in True Blood and MacDonald has been cast in the Boardwalk Empire pilot), but overall I think all of these names are decent possibilities.
Update: Smoldering Hound has left a comment stating that the list is still a work in progress. You can still head over to the forums and vote for the different candidates, or if you don’t like any of the choices, post some of your own!