So far from what I can remember they have several choices in the rumor mill:
Orlando Bloom
Clive Owen
Gerald Butler
Christian Bale
and another one I can't remember who
From the rumor mill, Orlando Bloom would be a good choice however a lot of people think he's just a tad too young looking to be a sophisticated spy.
Clive Owen and Gerald Butler have the right age, just not the recognition yet, although that might change this year. Clive Owen is more the favorite right now, especially since he's well known in Britain, known in the US from the BMW shorts and he has the look and attitude for Bond.
Gerald Butler may be on the rise especially if he does well in the Phantom of the Opera coming out this year. Agewise and looks are pretty good on that part too.
Christian Bale is the wildcard of the bunch. He's young looking but not so young that he could pull it off. He's got talent and americans know him from American Psycho and Reign of Fire. If the new Batman movie comes out and fares well, it could be the boost that Christian Bale needs to put him in the forefront of people's minds.
Anyway... this is still just speculation.

Whoever they get, Sean Connery will always epitomize Bond for me.