This was on my local NBC affiliate, so I don't have a link. Below are the twelve worst, and by the way, washing or peeling them doesn't make a difference. If possible, always try to buy the certified organic versions of these vegetables.

peaches
apples
sweet bell peppers
celery
nectarines
strawberries
cherries
pears
imported grapes
spinach
lettuce
potatoes

And here are twelve that had no, or almost no, detectable traces of pesticides:

onions
avocados
frozen sweet corn
pineapples
mangoes
asparagus
frozen sweet peas
kiwis
bananas
cabbage
broccoli
papaya