Groupon - Each day Groupon offers a deal through local vendors in your city.
Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything
idealo - Idealo is a free to use mobile application that helps you to find products, compare price and make an informed decision.
Honey - Honey is a browser extension that automatically finds and applies coupon codes at checkout with a single click.
Mobile Bandit - Don't Buy Deals get Mobile Bandit.
Dealspotr - Dealspotr is like Wikipedia for deals.