Mars Science Laboratory was to be the big thing in 2010, but they blew the deadline along with the budget, and now it's delayed to 2012.
On the bright side, the Kepler space telescope should finally put out some results on its search for extrasolar planets. It's not eye candy, and it won't be until later that it finds how many Earth-sized planets are in Earth-sized orbits around stars, but next year we'll finally get some statistically-valid information on the percentage of stars with planets in short-period orbits.
And then there's WISE, the Wide-field Infrared Survey Explorer, a space telescope that launched yesterday. Other telescopes are more sensitive for detecting cold objects in space, but they can view only tiny parts of the sky, while WISE will survey the entire sky. That means it could find brown dwarfs (massive planets/failed stars) or stray gas giant planets that are closer to our solar system than the Centauri star system, the closest known stars that are four light years away.
If WISE finds a brown dwarf within .5 light years or less, I think it's conceivable that a robotic mission to explore it could be launched and arrive there in this century. If aerocapturetechnology gets sufficiently developed, it might even go into orbit instead of being a flyby.
Not exactly a mission to another star, but pretty close.
UPDATE: Cool Cassini pic of sunlight on a lake on Titan. No one has ever seen sunlight on a lake anyplace besides Earth, until this picture was taken. I guess we will have some eye candy in 2010.