When should you buy organic?

As an environmentalist, I am a big supporter of buying organic, but I often wonder what foods do i really need to worry about, and which foods are not worth the extra pennies it costs me to buy organic. Serously, with how many bananas my 7 room mates and i go through,
sometimes It is hard as college students to take the green route.
I was very interested to see a post on apartment therapy about this very thing.
(Bananas Aren't on the list, yay!)

Below are 12 fruits and veggies that the Department of Agriculture announced to have higher levels of pesticides, even after washing. The results are based on an analysis of government tests by the Environmental Working Group (EWG), a research and advocacy organization based in Washington, D.C.

Here are the must-buy organic fruits:
Apples
Cherries
Grapes, imported
Nectarines
Peaches
Pears
Raspberries
Strawberries

Vegetables:
Bell peppers
Celery
Potatoes
Spinach/lettuce
Don't worry about going organic with these fruits:
Bananas
Kiwi
Mangos
Papaya
Pineapples

Vegetables:
Asparagus
Avocado
Broccoli
Cauliflower
Onions
These generally don't have pesticide residue.