CardStar is an iPhone app from Mesa Dynamics that allows you to enter in your grocery store, drug store, and gym card barcodes for scanning at the stores. I love the idea of ditching store cards and using my iPhone instead. I’ve used it several times at Kroger (doesn’t seems to work with the self checkout scanners, but it works great at the regular registers) and will try it out at the gym soon. The best part of CardStar is the price, free! There are lots of mixed reviews, so your milage may very.