Blue Nile Coupons. Get Coupons, Promo codes, Coupon codes & Deals Online Free for Blue Nile store. Save money with promo codes for Blue Nile store. Shop and Save with Coupons & Cash Back. Blue Nile is the largest online retailer of diamonds and fine jewelry. As Forbes’ Favorite Online Jeweler (every year since 2000), we offer outstanding quality, selection and value. We feature free shipping and 30-Day Returns on every order.