This is a great example of NASA getting good bang for the buck on a low budget:
Deep Impact extended mission heads for comet Hartley 2
"NASA has given University of Maryland scientists the green light to fly the Deep Impact probe to Comet Hartley 2. The spacecraft will pass Earth on New Year's Eve at the beginning of a more than two-and-a-half-year journey to Hartley 2. During the first six months of the journey to Hartley 2, they will use the larger of the two telescopes on Deep Impact to search for Earth-sized planets around five stars selected as likely candidates for such planets. Upon arriving at the comet, Deep Impact will conduct an extended flyby of Hartley 2 using all three of the spacecraft's instruments — two telescopes with digital color cameras and an infrared spectrometer."
Found via Slashdot.