The Dawn spacecraft will be launched on a mission to the asteroid belt in a few days. Check it out at the Dawn website.
Dawn will be the first spacecraft to orbit two separate bodies after leaving the earth. This is a rather difficult thing to do, and the craft can manage it using ion engines: their thrust is low but they are extremely efficient in their use of propellant (more technically: the specific impulse is very high). You leave them switched on more-or-less permanently, and after a few months you are either going like the clappers, or have climbed further out of the gravity well of the sun (or some other body) ... or both.
The targets of the Dawn mission are the two most massive asteroids, Vesta in 2011 and Ceres (now officially classified as a dwarf planet after the recent shakeup in naming) in 2015. These two are about as different as asteroids get, in their characteristics, and so if one is to choose only two targets, this pair is a good pick.
Good luck to the Dawn team ...