On our budget I just can't buy everything organic; it's too expensive! Even the Farmer's Markets in our area are not too cheap, so I use the Environmental Working Group's list of foods that are musts when it comes to buying organic. The reason: these foods don't have enough protective layering to prevent pesticide contamination.
You can go to their site for a list of the Dirty Dozen, foods that should either be bought organic (pesticide-free) or else avoided. They also have a list of produce that is fine to buy non-organic, the Clean Fifteen. I love having both lists so that I know when I can get cheaper produce without worrying about the pesticides.
Keep in mind, this list only refers to the pesticide content; it is not a guide for genetically-modified organisms. I can't currently handle the stress that all entails, so I'm just sticking to the pesticide issue for now.
Here's the lists typed out, in case you want to just copy, paste, and print for your binder to keep the list handy:
Dirty Dozen Buy Organic!
sweet bell peppers
Clean Fifteen Non-Organic ok!
And as always, produce that is in season is cheaper and better-tasting. If you eat following the seasons, you'll provide your body with a good variety of vitamins and minerals; the way God made it to work for us!