keisha castle-hughes? for Arya? she's Maori... Arya's a pale northern european type of girl...i mean as much as she and jon are meant to look alike, they are still brother and sister (or at least cousins if we believe the R+L=J theory) and they are still the same race as their other siblings...
Hayden would make a far better Sansa i think - little, innocent looking, can play clueless-but-not-stupid well... she's a little heavy looking to play Dany (and i don't mean fat - Dany should be a slip of a girl, and Hayden is not a slip of a girl - besides, Sansa needs to be as beautiful as Cersei was as a girl, and likely to surpass her as an adult Hayden is gorgeous)
Johnny Depp is far too old to be Renly.
so is Zachary Ty Bryan for Robb - he's also got a white-trash thing going on that wouldn't sit well with the King in the North.
as much as Kristin Kreuk is gorgeous, i think she looks too old to be the innocent idealistic Sansa, however she would make an even better Shae than Megan Fox. her colouring matches my image of Shae better than Megan Fox (who would likely make a great Margeary)
Orlando Bloom is WAY too old to be Loras.
For Jon Snow, i believe the only young actor who could portray him well atm is Shia LeBeouf. He's a little old, but he plays 16 well in most things he's in anyway...
Nicole Kidman for Cersei for sure (this goes against my usual practice of not choosing actors who've been in Fantasy films before - since NK is in Golden Compass and Mrs Coulter is not too disimilar a character than Cersei - but she was floated as best to be cast as Cersei before she was in Golden Compass... so its a great idea).
If your casting Nicole Kidman as Cersei than the very best choice to play Jaime is Daniel Craig - they have the most electrifying chemistry on-screen.
Viggo as Bronn isn't a bad choice either - at least looks-wise, i detest Viggo as an actor - though i may reconsider that position after i've seen Eastern Promises (i've heard good things of him in it).
overall your casting is way too old for most of the younger characters, and is made even more apparent when you cast actors who look as young as Daniel Logan or Keisha Castle-Hughes do beside them in roles that are essentially the same age.