There is a board game which is released with expansions for almost every book. It has many similarities to Diplomacy. The one I played includes, Stark, Greyjoy, Baratheon, Lannister, Tyrell, and potentially Martell depending on how many players there are. Tully, Arryn, and Targaryns are not included, but neutral armies occupy each of the major cities of the Eyrie, Kings Landing, and Sunspear.
http://boardgamegeek.com/image/120724/a-game-of-thrones
I'd think that playability would be best with Stark, Greyjoy, Baratheon, Lannister, Tyrell, Martell, and Aryn, and possible neutral armies in Kings Landing and Riverrun. Otherwise I agree with most of what Ruffhaus said. Somehow the newest version manages to cram in the Targaryns and the Tullys.
http://boardgamegeek.com/image/187579/a-game-of-thrones