Considering that he is changing the focus from Iraq to Afghanistan, Kabul might be an option. Unlikely though.
Tehran, Iran is unlikely. Regardless of how the rest of Iran's governmant may be, Ahmahdamnnutjob is making them look just slightly less cartoonish than North Korea.
Pakistan .. no.. just .. no. For a hundred different reasons, that'd be a shitty pick. Not the least of which is security issues.
Mecca - No, he's not a Muslim. You want to start World War V, VI, and VII all at once .. have the President of the Great Satan show up in Mecca. The Muslim lunatic fringe would just snap.
Baghdad - Possible. He could show up there to showcase the place as a "Beacon of Democracy" in the middle east, or somesuch noise. Though I think he is neither talented enough to spin that just yet, nor foolish enough to think he can.
Riyadh - Possible, but unlikely, considering Saudi Arabia's positioning lately. Nothing to be gained by showing up there, and only a loss of face by appearing to give in to Saudi's current rhetoric.
Riyadh would be a brilliant choice if he could pull an interesting trick out of his ... hat. If Obama were to show up in Riyadh, and jointly announce that the Kingdom of Saud and the USA were taking a joint leadership position in a "new age of peace and prosperity in the middle east..< blah blah blah >"... but there's about zero chance in hell of the Saudis taking such a front-and-center overt role in the middle east, unless things under the surface there are much much worse than they look. Saudi takes a overt leadership role in the M.E., and they run a very real risk of losing the balance of control they currently have.
Whatever he does, here's to hoping he is listening to his foreign culture advisers - 'cause the Western mind does NOT run on the same tracks as the Middle Eastern mind.