Another option (other than Green Ronin's A Song of Ice and Fire game, as mentioned) is Guardians of Order's A Game of Thrones setting book - either OGL [d20], or deluxe, the latter being dual-statted in d20 and Tri-Stat. This was released a while back though, and might be difficult and/or expensive to purchase. Not sure. Regardless, it's rather good - as far as d20 variant systems go - and does a decent job of matching system to setting, to the extent that said base system allows.
Personally, I find 4e distasteful enough as it is, but can see types of settings for which it might prove adequate. . . A Song of Ice and Fire certainly not being one of them, however. YMMV, etc.