The cool news is that - to some extent at least - the folks in charge are willing to listen to the fans' opinions. So, if you have some ideas for who should play Jaime Lannister and Bran Stark, get yourself over to the new forum at Westeros and make your feelings known. According to GRRM, David Benioff and Dan Weiss from the production team are regularly dropping by the forum to check out the suggestions, so it's a chance to have your voice heard.
Personally, I don't have any particular recommendations - my knowledge of TV/film actors/actresses isn't good enough. However, I would like to see Cillian Murphy in some sort of role, because I think he's a top actor.
There's also a new unofficial blog dedicated to the TV adaptation of the series, so check it out for news and opinion.