Read a great article today about the fruits and vegetables to avoid because they are susceptible to pesticide contamination: http://www.cnn.com/2010/HEALTH/06/01/dirty.dozen.produce.pesticide/index.html?hpt=Sbin
Here's a quick recap:
Sweet bell peppers
Spinach, kale and collard greens
Try to buy only organic from this list, and be sure to ask at the farmers' market to be sure that they haven't used pesticides -- surprisingly, one farmer said to me that she still uses pesticides, just not as much!