The "clean fifteen" are fruits and vegetables that retain little pesticide or are not treated with pesticide ( or a very small amount).
These are the fruits and vegetables that you can risk buying non-organic. Generally these have thicker skins like kiwi and melon. These also include grapefruit, eggplant and cabbage. Since organic is often more costly then conventional, you can save some money by buying conventionally grown "clean fifteen" and organically grown "dirty dozen".
You can also save money by buying organic frozen fruits and veggies. Frozen fruits are a great snack. Frozen vegetables can be even more nutritious then fresh as they are frozen right in the fields, retaining most of their vitamins and minerals. Fresh veggies often travel long distances and lose nutrients through exposure to heat and air. Just remember whatever you cook, frozen or fresh, use as little water as possible and cook for as short a time as possible.
And when you wash your fresh veggies and fruits, don't waste money on produce washes, plain water is more effective.
Find the guide at http://static.foodnews.org/pdf/EWG-shoppers-guide.pdf