I just finished reading this New York Times article about easy ways to go organic. For a long time, I kept a beat-up old photocopy of a chart showing which fruits and vegetables had the most pesticides, but it got lost in the move, and was from 1993 anyway. But it was really useful in considering which produce I should always buy organic (for instance, I now only buy organic or pesticide-free strawberries).
So this article offers a short and sweet summary of five foods that you should always buy organic. The list is milk, potatoes, peanut butter, ketchup, and apples. The only one of those I would have guessed is milk, so this article will certainly impact the way I shop.