Cersei is “as beautiful as men said.” She has long golden hair and emerald green eyes. Her smile looks fake to Jon (and GRRM implies it would look fake to any adult, by saying “even at fourteen” Jon can see through it — although it could just be Jon’s preternatural bastardly maturity, of which more later.)
Myrcella is “a wisp of a girl, not quite eight” with long golden curls.
Tommen is plump and has white-blond hair that is longer than Arya’s. We learned in Catelyn I that he is seven (which would make for some pretty close birth spacing between him and Myrcella — I almost feel sorry for Cersei).
Joffrey is twelve, taller than fourteen-year-old Robb who has himself been described as notably tall. He has long, thick blond curls, emerald green eyes, and pouty lips.
Jaime is “tall and golden, with flashing green eyes and a smile that cut like a knife.” And of course, Jon thinks he looks like a king should look. I use this, along with the image of Jaime sitting on Arys’s throne after assassinating him, is the basis for my “Jaime will end up King” theory. (No, I’m not serious, and am too lazy to try to come up with political/military circumstances that could allow this to happen — just having fun as a confirmed Jaime fanperson. Really, I think he’ll end up perishing in some form of suicide-by-cop while symbolically trying to do his job as Kingsgaurd by defending a king who he ironically doesn’t like or respect much, such as maybe Stannis. Hopefully not until very near the end of the series, and not until after strangling Cersei.)
Tyrion gets more description than any of the others:
“[H]alf his brother’s height … [with] stunted legs. His head [is] too large for his body, with a brute’s squashed-in face beneath a swollen shelf of brow. One green eye and one black one peered out from under a lank fall of hair so blond it seemed white.”
And of course, there is the final line of the chapter–“just for a moment, Tyrion Lannister stood tall as a king”–undermining my Jaime for King campaign before it even started.
Interestingly, both Tyrion and Tommen have white blond hair, while the rest are described as golden. Tommen’s biological parents are siblings, Tyrion’s (if we assume they’re exactly who they’re supposed to be) first cousins; it seems like the Lannisters may have a recessive white-blond gene floating around and these two got a double dose. Tommen’s white-blondness does undermine those who would use Tyrion’s white-blondness as evidence that he’s actually a Targaryen, unless they want to argue that Tommen is a Targaryen too. (I never liked that theory, if only because it makes Tyrion’s relationship with Tywin less artistically satisfying to me if Tywin’s not really his dad. Tywin doesn’t get a loophole for treating him badly, nor Tyrion a loophole for kinslaying.)