The one food I've purchased in its organic version exclusively for the last 5 years has been strawberries. I read a while back that pesticides in conventional strawberries were through the roof. And their irregular surface made washing not very fruitful.
Since then, the Environmental Working Group (EWG) did a little more testing that resulted in their "Shoppers Guide to Pesticides in Produce". Visit their online report for details. Or download their handy wallet guide (pdf).