The picture I've been getting over the recent weeks would be that it would be Jenson Button and Nico Rosberg at Brawn GP, Nicolas Hülkenberg and Rubens Barrichello at Williams and Lewis Hamilton and driver X at McLaren.
I think Nico Rosberg isn't the one to go to McLaren because his father Keijo "Keke" Rosberg told his opinion that it would be Kimi Räikkönen who would go to McLaren. I doubt very much Keke would say that if he would know his son would be going to McLaren or would be in contention for that seat. Keke just never has seemed like someone who talks BS about the driver moves so I will take his words as pretty convincing. So what I gather from what he has said is Nico is not going to McLaren. As we are pretty sure by now Nico is leaving Williams, and that he would be moving "up", the only realistic choice I see is Brawn GP.
Jenson - I doubt very much he would risk changing teams now that he has found the one to win with. He will stay at Brawn GP. He is their "homie"

Rubens is happy to get more time in F1, he is very strong, a bit superstitious, but that minor detail pushed aside, someone like Williams can use him, and the team too, can use him

If he can win a GP for Williams then he will climb up a notch or two in the hero list. I think that goal would be enough for him - he may not get another chance to win the WDC, but he may get many chances to win Grands Prix and what a better place to do that than Williams, a team once so heroic but needs something a little bit extra nowadays to win - perhaps that little bit extra could be Rubens? I hope he will win many Grands Prix still.
Who could that driver X at McLaren be? I would say it very likely will not be Heikki Kovalainen. All said and done, his performances have been disappointing. Yes, the team was gathered around Lewis before he had even visited the McLaren Technology Centre, but Heikki, did you let it get in your head a bit too much. Don't look to the other side of the garage that much.
I saw some of his interviews in Finnish and he looked and sounded like he knows he will be out of the team. I'll keep cheering for Heikki no matter what and he just needs to go to another team and keep working. It will come to you Heikki - don't doubt yourself so much

you've had a fantastic attitude, at least what I've seen, so you just keep working hard and it will come to you. Remember how short a time you've been in F1 - look at Häkkinen, he spent years at McLaren not winning anything, even getting his first win as a gift. You've still got many more years to show everyone Suomussalmi is not a place of wimps
So, who is the driver X? Kimi Räikkönen? Could well be. I just hope they would let us know already. McLaren, sort it out for us by UAE, thanks. There are many other good candidates but I don't think they can find a better one than Kimi - Lewis you have already and Fernando will be at Ferrari. So of the Super 3 you only have Kimi available to you and I would be surprised if you don't do all you can to hire him