SO2 is polar. Although oxygen and sulfur are both highly electronegative, oxygen is more electronegative than sulfur. Therefore, oxygen-sulfur bonds are slightly polar due to oxygen exerting more control over the electrons in the covalent bond.
However, molecules are not necessarily polar just because there are polar bonds present in them. The reason that these polar bonds make SO2 polar is that the molecule is also bent, similarly to H2O, and is positioned with sulfur in the middle. Therefore, the molecule is not completely symmetrical. The side that has both oxygen atoms pointing toward it is partially negative, and the side that has a sulfur atom has a partial positive charge, causing the molecule to have a polarity.