Here's a list of produce that you ought to purchase organic due to high levels of contamination: pears, apples, strawberries (most berries), nectarines, cherries, bell peppers, coffee, celery, lettuce, spinach, grapes, raisins, potatoes, and tomatoes.
(Coffee is the big one here. It's been stated that if you were to buy only one thing organic, you better make it coffee since most of it is grown in third-world countries where the laws are less stringent and many use harmful pesticides such as DDT, which is a known carcinogen and outlawed in the US.)
Pears and apples have the highest levels of contamination of all produce, and apples are the second most commonly eaten fruit in the US.
Some produce presents very little risk of contamination to you, and can thus be bought conventionally: asparagus (fewer pest threats), avocados, bananas, broccoli (fewer pest threats), cabbage (requires less spraying to grow), sweet corn, sweet peas, cauliflower, kiwi, mango, onions (less pest threats), papaya, and pineapple. Obviously, eating all organic produce would reduce your exposure to pesticides the most, but by sticking to the above lists, you can be sure to get the most bang for your organic buck.
le thé tout comme le café n'est pas en reste au niveau des pesticices:
par 
