Receipt Hog

Simply take pictures of your receipts (doesn't have to be just groceries) and earn coins.  The coins can then be traded in for an Amazon gift card, money in your PayPal account, or magazines.  Receipts that don't earn coins give you entry into their sweepstakes.

iBotta

I love this app!  It does take some time to browse through their offers, but you can do this while brushing your teeth or during commercials of a tv program.  You earn money on products that you might buy anyway.  If you don't want to go to the trouble of finding offers in advance, simply do a product search after your shopping trip and see if an offer is available (this way, won't be tempted to spend on something that wasn't on your list just to save $0.50).  Connecting to your Facebook account creates teams for bonus savings.

ncp mobile

Scan the barcodes of products and enter in your total amount paid.  This app earns you points which then ca be used to shop in their prizes catalog.  You also can take surveys about your shopping habits for additional points.

e-rewards

At www.erewards.com (also has an app), you can take surveys to earn virtual money then trade in that money for various prizes and gifts.  We use our survey money for Hilton Honors points.  Last summer, my husband and I took a 12-day road trip and were able to use our points for all but two nights.