Petraeus and Mattis may take command of Centcom and Iraq
The Washington Post in its story about Abizaid's decision to retire gives some hint at his replacement.
...These two generals have received the best reviews by the critical media and are prominent heroes in books that have been critical of the effort in Iraq. In both Cobra II and Fiasco they both come off as insightful and intelligent. BTW, Petraeus, who has a PhD, chose pop tarts over MRE's often in the march to Baghdad. Mattis has received criticism for being too enthusiastic about his job in Afghanistan and Iraq, but few can deny that he is very good at it. Both have been participants in the redraft of the military's counter insurgency doctrine.
The widespread expectation within the military has been that Abizaid will be succeeded by Lt. Gen. David H. Petraeus, who led the 101st Airborne Division in the invasion and early occupation of Iraq and later returned to head the effort to train Iraqi army and police forces. Gen. George W. Casey Jr., the top U.S. commander in Iraq, is also expected to leave his post in the spring, and some Pentagon officials predict he will be followed by Marine Lt. Gen. James N. Mattis. Casey is another candidate to replace Abizaid, one senior military official said. But all those moves will be dependent on the approval of Gates, whose views on the personnel changes are not well known.