Certain produce items tend to be highly contaminated with pesticides (try to buy these organic), while others tend to be relatively low in pesticide residue (you can save money and buy these conventionally).

     The Dirty Dozen: Top 12 Foods to Buy Organic listed in descending order, starting with greatest levels of pesticide contamination:

    Peaches, Apples, Sweet bell peppers, Celery, Nectarines, Strawberries, Cherries, Pears, Grapes, Spinach, Lettuce, Potatoes

    The Cleanest 12: Save Your Money & Buy Conventional listed in ascending order, starting with of lowest levels of pesticide contamination:

    Onions, Avocados. Sweet corn (frozen), Pineapple, Mangoes, Asparagus, Sweet peas (frozen), Kiwis, Bananas, Cabbage, Broccoli, Papaya

     I would say that the next best option is frozen organic

    Freezing is a very efficient method of preserving the nutritional value, texture and flavor of most vegetables. Vitamins will keep in frozen vegetables as good or better than fresh. In some cases frozen may be better as light exposure and other transportation and storage conditions may degrade the quality of fresh produce.