According to Deadline The Dark Knight director Christopher Nolan, who has been placed in a ‘Godfather’ role to the Superman reboot, is currently meeting with a number of potential directors and will submit his choice to Warner Bros. within the next few weeks. David Goyer came up with the concept and wrote a script with Jonathan Nolan, but now the Batman team will be handing the directorial duties to someone else.
The names mentioned include Duncan Jones (Moon), Jonathan Liebesman (Battle: Los Angeles), Matt Reeves (Cloverfield), Tony Scott (Unstoppable), and Zack Snyder (Watchmen).
Out of the directors above I think we can rule Liebesman out as he just signed to direct Clash of the Titans 2 and will be unavailable. Zack Snyder could also be busy as he plans to direct Xerxes, a prequel to 300 which is currently in the scripting stage, although he could delay that or let someone else direct if Superman takes his fancy.
Tony Scott has been hit and miss over the years, so I would go for one of the two up and coming directors: Duncan Jones or Matt Reeves.
Apparently Warner Bros. has to get the movie made by 2012 as the studio stands to lose certain rights to the heirs of Superman creator Jerry Siegel. Filming will almost certainly begin next year so that it can hit its Christmas 2012 release date.