The Environmental Working Group publishes something really useful called the Shoppers Guide to Pesticides. In it, they offer two handy lists: (1) The Dirty Dozen -- conventionally grown produce items that contain the most residual pesticides, and (2) The Clean 15 -- conventionally grown produce items that contain the least residual pesticides.
While we believe that organic is always best, there nonetheless are times when most of us (for whatever reason) consider purchasing or consuming conventionally grown (meaning "sprayed with pesticides") produce.
Read more: Mnemonic for the "Dirty Dozen" Foods that You Should Only Buy if Organic!