Dawn spacecraft is nearing Vesta and is planned to go into orbit 16 July. http://science.nasa.gov/science-news/science-at-nasa/2011/06jul_vestamoon/ The craft will orbit Vesta for several months and then move on to another asteroid, Ceres. The NASA press release mentions that several asteroids have been found to have moons. For example Ida has a tiny moon. A photo of Ida and its moon is included in the release. Also an early picture taken by Dawn of Vesta itself.