The fastest Probe we could build now I found this at 
http://www.nature.com/news/the-exoplanet-next-door-1.11605


  Even when launched by one of the most powerful rockets on Earth, boosted by a gravitational slingshot around Jupiter, and further accelerated by a radioisotope thruster, that probe would take about 28,000 years to reach α Centauri. Quoting British author Douglas Adams, McNutt quips: “Space is big. Really big.”


Is this still the fastest we can get right now?
For small values of practical an interstellar Orion craft could achieve ~3.3% c (~133 years to Alpha Centauri, one way with no deceleration at the end of the trip)). Which is in principle within reach of present technology if we chose to pursue it. But cost and aversion to nuclear technology on such an extravagant scale make it unlikely that we will see Orion space craft of any ilk built in the foreseeable future.