I've known of some foods that one should try to buy organic, because of how heavily they receive pesticides (raspberries, peanuts/peanut butter). I've known of other foods where it isn't as much of a concern, because there is an outer skin (oranges, bananas). I read a helpful post on Whole Food nation summarizing what types of you should try to buy organic and which are ok being non organic. I summarized the info below but there is additional helpful info in the original post, including why certain foods should be bought organic and how many pesticides are sprayed on the foods (most are 25 or more).
Non organic is ok:
Organic is safer:
Beef, Pork and Poultry
Milk, Cheese and Butter
Strawberries, Raspberries and Cherries
Apples and Pears
Spinach and Other Greens
Peaches and Nectarines
Red and Green Bell Peppers
I would like to add that I believe buying local produce when you know how it is grown (like from a CSA) can provide a happy middle ground to the expense of organic and the lack of quality and nutrients of the non organic, conventionally grown items above. Cost is unfortunately prohibitive of our buying more organic.
Are there particular foods you regularly buy organic? There are some for Ryan and I, though I don't think there are any foods we always buy organic. I prefer organic raspberries, for the lack of chemicals and because I have found them to taste immensely better. We have never bought organic meat. By the way, don't be fooled by "all natural" or "100% natural" labels on chicken - there are no established guidelines for what constitutes natural.