After several delays in recent months, NASA is set to launch the space probe Dawn on Thursday 7:20 a.m. EDT on an eight-year mission to unlock the secrets of the solar system and how it was born. Dawn is scheduled to enter orbit around asteroid Vesta in October 2011, and then begin orbiting dwarf planet Ceres in February 2015.
Dawn Mission Home Page

Asteroids – very comprehensive guide from nineplanets.org