I recently became aware of the Environmental Working Group (EWG) and have been very impressed with their work. The first iPhone application that I downloaded from them was a list of the best to least healthy sunscreens and now they’ve added another app that will help you decide which foods to buy organic. There is also a pdf version of their list that is available on the EWG website.
Buying organic is best, but it is also expensive. There are some foods that hold the pesticides in more than others. When buying these foods you should opt for the organic. The list produced by EWG list the foods that contain the most pesticides and foods that have the least.