PG: Chris Paul/Deron Williams/Derrick Rose
SG: Dwayne Wade/OJ Mayo
SF: LeBron James/Kevin Durant/Danny Granger
PF: Carmelo Anthony/Chris Bosh
C: Dwight Howard/Brook Lopez
Alternates: Blake Griffin, Stephen Curry, LaMarcus Aldridge
The PG group is self explanatory, Chris Paul and Deron Williams are two of the best PG's in the world and Derrick Rose will be near/at that level by 2012.
The SG spot is the hardest, I doubt Kobe has another Olympic campaign in him. Wade will also be 30 by then so he may decide to stay out but I don't think so. He'll be the starter and OJ Mayo's game will be similar to Kobe's by 2012 and will be able to fill that spot. Curry may take Granger's place and be the "designated shooter" but I'm not sure.
LeBron and Durant are pretty much locks for any national team they decide to play for. The question is will there be a need for a Tayshaun Player (Granger kind of) or will a Redd type of shooter (Curry) be more important?
Bosh and Griffin will be the premier young PF's by the time 2012 comes around. LMA will be the alternate if Griffin suffers from the likely career ending Clipper injury.
Howard is a lock, I think by default Lopez will have the other spot as there just aren't any young C's out there anymore. If Hawes continues to improve then he'll be fighting for the spot along with Lopez.