Here is the Dirty Dozen, the top 12 fruits and veggies that I most highly recommend that you purchase organic because conventional produce is sprayed more heavily with pesticides:
Dirty Dozen:
Apples
Celery
Tomatoes
Cucumbers
Grapes
Nectarines
Peaches
Potatoes
Spinach
Strawberries
Blueberries
Sweet Bell Peppers
Also: Green beans and kale are moving up on the most sprayed list as well.
Here are the Clean 15. These are the fruits and veggies that you can eat conventionally because they are not sprayed as heavily with pesticides.
Clean 15:
Onions
Avocado
Sweet Corn (watch for GMO)
Pineapple
Mango
Sweet Peas
Eggplant
Cauliflower
Asparagus
Kiwi
Cabbage
Watermelon
Grapefruit
Sweet Potatoes
Honeydew Melon