I personally have never used this before but TONS of bloggers recommend it.
When you join Nielsen Home Scan Consumer Panel here is how it work:
Panel members are provided with a hand-held scanner, and then every time you or members of your household shop, you’ll use the scanner to scan the bar codes on all of your purchases. Upload your data to Nielsen once a week to earn gift points that are redeemable for name-brand merchandise, including electronics equipment, jewelry, household items, toys, and much more!
You can check your zip code and see if you are eligible by clicking here.