Casting so far has brought me nothing but joy-- Sean Bean and Peter Dinklage are the only ones listed who are familiar to me, but they're both perfect for their characters and for the most part I'd rather see everyone played by no-names anyway.
Over at grrm (the author's blog), there's been a guessing game regarding a few more parts that have been cast: since he's not allowed to reveal the names yet, he kindly offered us some hints instead. A few of the names that have come up in response to the hints are David Boreanaz, James Marsters, and Summer Glau, and while any one of those three is probably too much to hope for, I'm still crossing my fingers. At the very least I feel like it's possible that some Whedonverse actor, however minor, will show up in the series at some point (provided it even gets past the pilot), and hopefully that will be enough to snag my fangirl friends and get you psyched about watching next year. :)
And now I just want to go on record saying that if any of these three do end up being correct guesses, Boreanaz should be Benjen Stark, Marsters should be Jaime Lannister, and Glau should be Daenerys Targaryen. I wouldn't object to them in other roles, but I'd be skeptical.
Seriously, someone else should read these books and then we can gush at each other about it for the next year. The only other work of fiction I've ever been so obsessed with is...Buffyverse. And Ice and Fire came first.
Eddard Stark is being played by freaking Boromir, guys. Tyrion Lannister is Trumpkin. BELIEEEEEVE.