the 12 items most laden with pesticides, and should preferably be consumed organic
Peach, Apple, Bell Pepper, Celery, Nectarine, Strawberries, cherries, Kale, Lettuce, Grapes (Imported), Carrot, Pear
On other lists, but absent in this dirty dozen, are spinach and potato.
and the Clean 15 (most of them have skins and are therefore 'safe')
Onion, Avocado, Sweet Corn, Pineapple, Mango, Asparagus, Sweet Peas, Kiwi, Cabbage, Eggplant, Papaya, Watermelon, Broccoli, Tomato, Sweet Potato.
you can download the guide here and take it with you when you go grocery shopping.
http://www.foodnews.org/walletguide.php