I'm totally impressed by Out of Milk. It's a shopping app that allows you to make and keep shopping lists for different stores, transfer purchased items to your "pantry" do you know what you've actually got and scan barcodes to keep a record of the prices you paid. I use it especially for Costco, since there are only certain items I buy at Costco. I can quickly build my Costco shopping list by referencing my saved "Costco" pantry.