Wow! What a summer! Dawn at Ceres, Rosetta and Philae at a comet perihelion! And my favorite, New Horizons at Pluto! All were launched in the previous decade, and all have now reached their primary mission. In addition to the mission websites linked above, the planetary society is writing timely and detailed updates on the missions.
Dawn is the first spacecraft to visit Ceres, the largest object in the asteroid belt. There are several very bright spots on Ceres which have drawn quite a bit of interest. Frankly, no one knows what they are.
Rosetta is not the first spacecraft to visit a comet, but certainly has the best camera so far. Plus, Philae, a little 100 kg lander successfully landed on the comet last fall and have enabled us to study comets far more than any previous mission.
New Horizons was the most significant, in my opinion, space probe to launch while I was in college, getting my aerospace engineering degree. We've never sent anything to Pluto, and our knowledge of Pluto is very vague. Only a few years ago in 2011 and 2012 did we discover the fourth and fifth moons of Pluto.
Just a note on orbital mechanics, in order to get to Pluto in only nine years, we can't really afford the fuel to slow down the trajectory and stay there. It's going something like 13.77 km/s, 30,800 miles per hour. The fuel required to slow down would cost hundreds of millions of dollars so the spacecraft was built without large fuel tanks to save money and designed to simply make a flyby.