Put a solar farm in geosynch...
...that is capable of generating several megawatts. Arm it with a very large pulse laser. After a couple of years/decades of flashing the asteroid, its trajectory should be sufficiently altered to ensure a miss. When the laser isn't being used to save the world, it can be used to accelerate interstellar probes, or the power can just be beamed down to earth to help pay the bills. All in all, I think this would be an extremely worthwhile endeavour.
Cheers,
Nathan.