It's simply that some of your normals that are wrong...
selectSelect all faces CTRL-ACtrlA, press CTRL-NCtrlN to recalculate the normals (or menu-> Mesh-> Normalsfrom the -> recalculate outside3d view header use Mesh > Normals > Recalculate Outside).
thisThis can happen when creating faces and selecting vertices in a different order than blender expects.