There are a few other main characters who haven’t been mentioned:
-Joffrey (sadistic evil incest king) is currently betrothed to Margaery Tyrell, ambitious daughter of another one of the powerful families of Westeros, although one we have seen less of. She definitely seems to want power, and is clearly playing him by pretending to be interested in crossbows and crypts and the other stuff he’s creepily obsessed with. Her brother is Loras Tyrell, the Knight of Flowers, a famously skilled knight who is also extremely gay. We have recently met their grandmother, Olenna Tyrell, who seems to be a crafty mover and shaker in her own right
-In addition to Robb (king in the North), Sansa (captive in King’s Landing) and Arya (wandering around with the outlaws), there are two other Stark children: Bran (young boy, crippled) and Rickon (younger boy, so far fairly irrelevant). They were in Winterfell (the Stark home) when it was captured for a while by Theon Greyjoy (who is now being tortured a lot). They escaped, and Theon killed two other boys and displayed their burned corpses so that everyone would assume they were dead and that he was thus to be feared. They are currently heading north towards The Wall in the company of a Wildling lady, a mystical boy, the boy’s sister, and Hodor (Hodor!), a large simpleton. Bran has all sorts of weird and presumably mystical dreams, and may be a “seer” or a “warg” or goodness knows precisely what.
-Robb (the king in the North)'s mother Catelyn is from the Tully family, yet another powerful family. The Tully patriarch just died, and he is survived primarily by his brother, The Blackfish, who seems pretty awesome, and his son Edmure, who seems like a whiney loser.
So, that’s the main plotlines going on. Now all we have to do is fill you in on Jorah Mormont, Barristan Semly, Shae, the Freys, Bronn, Sir Ilyn Payne, Missandea, Davos Seaworth, Mellisandre, Hot Pie, Gendry, The Mountain, Jon Arryn, Grand Maester Pycelle, legendary lover Podric Payne, Roz the exposition whore, Balon Greyjoy, Yara Greyjoy, Tommen and Myrcella, the Kingsguard, the Dothraki, Qarth, the mountain clans, that pirate whose name I don’t remember, and Robin Arryn (whose name in the TV show might be different), and you’ll be totally caught up!