It's a been a long, difficult road, but the Dawn mission launched this morning and is on its way to the asteroid belt. It will go to Vesta and Ceres, the two largest asteroids, orbit them, and take lots and lots of data. The images will be simply spectacular, and it will also take spectra and mineralogical studies to determine the composition and history of these two ginormous rocks in space (Ceres is about 1000 km across, Vesta 500).
Search for the word Dawn in my blog search engine to get an idea of how tough this mission has had it: it was basically canceled, then reinstated, then delayed, and and and. My friend Amara has an excellent blog post with some more background.