The nonprofit Environmental Working Group studied 47 fruits and vegetables and ranked them according to contamination.
You can get the iphone app of this list or a .pdf at their web site.
Use the list when you shop to determine which organic produce you should be buying.

Serving Size: 1/4 cup
Yield: 12 servings

Ingredients:
2 cups seeded and chopped fresh melon, honeydew, cantaloupe or watermelon, (use one kind or a combination)
1 cup peeled, seeded and chopped cucumber