*Mod Note* Guys this thread is fine to stand but please be aware that non-book readers might stumble in here, so with that in mind try not to spoil future events and use tags please, if it's a case where you feel you would like to discuss future events in season 3 and how they might pan out on screen with the knowledge of the books, I think maybe a general season 3 book readers thread might not be a bad idea? I'll edit the title to add more warning maybe too.
http://ie.ign.com/articles/2012/05/29/game-of-thrones-new-season-3-characters-revealed
With production set to resume this summer, Entertainment Weekly have a list of characters from the books slated to appear in Season 3. Executive Producers David Benioff and D.B. Weiss have made it clear in the past that due to how jam-packed the novels are, they will not necessarily be doing exact book-by-book adaptations as much as pulling different elements at different times. This includes a couple of characters on the list below, who fans of the books know were introduced in the second novel, “A Clash of Kings,” but didn’t make it into the second season.
Benioff tells EW, “[Jojen and Meera Reed] haven’t been written out. It’s important to point out that that we have the largest cast on television right now. We introduced dozens of new characters in season two. If you hurl 300 characters at an audience, the story collapses under the weight of too many faces, too many names, and too many subplots. We need to be just as mindful of the audience members who have never read the books as we are of the readers; the series will fail if we only appeal to those who already know the characters. So we try to be parsimonious about how many new roles we introduce to the story and when we introduce them.”
While the showrunners stress there will be more beyond this, characters certain to show up in Season 3 include:
Mance Rayder: Former Night’s Watch member turned the Wildling “King Beyond the Wall.
Daario Naharis: Captain of the mercenary group, Stormcrows.
Jojen Reed; Meera Reed: A teenage brother and sister with connections to the Starks.
Edmure Tully: Catelyn Stark’s brother.
Ser Brynden Tully (The Blackfish): Catelyn Stark’s uncle.
Selyse Baratheon: Stannis Baratheon’s wife.
Shireen Baratheon: Stannis’ daughter.
Olenna Redwyne (The Queen of Thorns): Margaery Tyrell’s grandmother.
Beric Dondarrion: Leader of the guerrilla group Brotherhood Without Banners. [It's been pointed out in the comments that we actually did see Beric once in Season 1, played by David Michael Scott. It's not clear yet if Scott will reprise the role in Season 3 or a different actor will play the character.]
Thoros of Myr: A red priest.
Tormund Giantsbane: A Wildling raider.