Project Daedalus

The trouble with the idea of launching a probe to a nearby star in the early 21st century is that it would likely take the probe hundreds of years to get to its destination, and in the meantime we are likely to develop the means to launch faster craft that would overtake the first one out.  Still, this proposal from the U.K. might have launched a probe to Barnard’s Star, 6 light years away, in only 50 years traveling at 12 percent of light speed. 

Links:

http://en.wikipedia.org/wiki/Project_Daedalus
http://www.daviddarling.info/encyclopedia/D/Daedalus.html