Update: American Express cardholders can take 10% off as well, via code AEXP16. Visa cardholders can take a rare 10% off at best-of-breed online jeweler Blue Nile via coupon code VISAW17. Blue Nile is the largest online jeweler, having sold over 50,000 engagement rings. They buy diamonds through the same wholesalers that Tiffany's does, but can sell for 20-40% less. As always, there is free FedEx, no sales tax and a fully guaranteed 30-day return policy.