This deal has ended.
Take 10% off at best-of-breed online jeweler Blue Nile via either coupon code VISAW17 for Visa cardholders or AEXP16 for those with American Express (both codes are now valid through 10/31). 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.