RetailMenot - The RetailMeNot mobile app allows you to find deals on the go for both online shopping and in store shopping.
Groupon - Each day Groupon offers a deal through local vendors in your city.
DontPayFull - Verified coupons and discounts for a variety of online retailers.
Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything
Offers.com - Offers.
Dealspotr - Dealspotr is like Wikipedia for deals.