According to GALLUP: weekly approval rating average for April 25, 2011 - May 1, 2011 is 44%. His average for his entire term so far is 51%. His highest was 69% in January 2009 and his approval ratings have hit a low of 41% several times with the latest being April 13-15, 2011.
In comparison, the average for a U. S. President in the tenth quarter of his Presidency is 55%. For May of the third year of the term, George W. Bush's approval rating was at 66%, and even Bill Clinton had a higher approval rating than Obama with 51%.
RASMUSSEN calculates it a little differently. They break it down into those who Strongly Approve of the job Obama is doing, which is currently 26%, with 35% Strongly Disapproving. Rasmussen subtracts the Strongly Disapprove rating from the Strongly Approve to obtain their Presidential Approval Index rating. In this case, it comes out to -9. Overall, 49% of the voters at least somewhat approve of the job Obama is doing with 50% disapproving. Rasmussen noted the numbers moved very little since the death of Usama Bin Laden.
REAL CLEAR POLITICS has his approval rating at 51.3% with 42.6% disapproving. They also have an excellent table comparing the major polls with each other making it easy to see the differences in the polling data.