I use a 1/2 x 1-1/4 x 4" combo whetstone with a medium coarse on one side and a fine or finish grit on the other, along with a spray bottle of water. I start with the coarse side, spin the wheel as fast as possible and still be finger safe and accurate where I have the stone. When I feel no hesitation or rough spots as shes going around, I switch to the fine side, rinse and repeat. Two times over the Summer, starting with the rotors fresh is plenty. You are only removing less than one ten thousandth of metal and all of the glaze in the process. Starting with a new rotor is the way to go, once they get seriously grooved, it's a lathe job or get a new one. Hardwickes Hardware at 42nd NE and Roosevelt Way in the U District is great place (all the flavors) to buy mechanic/machinists stones, along with any other tool you might fancy. It's absolutely the best tool store, I have ever been in. I should have mentioned, flush your brake pads with Brakeclean or a garden hose, before you ride and hit the brakes.
