toothbrush
Thats exactly what I used, a soft bristle toothbrush ever soooo gently. My radiator usually looks like a serial killers lifetime insect collection by the time I get home from a ride. I got sick of that really fast and just ordered the Evotech radiator guard for $100 shipped direct from Evotech through ebay. Its about $20 more than the next cheapest, and $30 more than the cheapest one available. IMHO, the Evotech definitely looks like its worth the little bit extra, its the only one that wraps around and covers the ugly sides of the radiator and the fit and finish just look top notch to me.