Consumer Reports recently published a guide (subscription required) detailing which fruit and vegetables contain the most pesticides. They recommend always buying organic when purchasing the following fruits and vegetables: Bell Peppers, Celery, Cherries, Grapes (imported), Nectarines, Peaches, Pears, Potatoes, Red Raspberries, Spinach and Strawberries. Their report was based on the free Shopper’s Guide to Pesticides created by the EWG (Environmental Working Group).
Also available is a downloadable wallet guide to produce. It lists the 12 popular fresh fruits and vegetables that are consistently the most contaminated with pesticides and those 12 fruits and vegetables that have low levels of pesticides.