A sundog. Sundogs are atmospheric phenomena that look like bright spots on either side of the sun. They usually formed by hexagonal ice crystals in cirrus clouds. See two relevant photos here and here.
Canon EOS 550D, 28/10/2011 16:54, Shutter Speed 1/1600, Aperture Value 9.0, ISO 100, Lens Canon EF70-200mm f/4L USM, Focal  Length 200.0 mm