Online auctions are a great way to get deals. There are traditional sites like Ebay, but you can also try more niche options. Poshmark is a hybrid auction site with a social network that allows you to bid and make offers, as well as follow other users' closets. However, since both sites are peer-to-peer, there's no verification that you're buying authentic items.
Another website similar to Butterfly Savings is Valpak. Your coupons can help you save 10 to 50% on purchases. There are great sites that list updated discount codes and limited offers. MoneySavingExpert is a good place to find them, since the codes are surrounded by smart spending tips, smart reminders to buy wisely.