Check out this Visa Discounts website. It is similar to American Express sync offers, but works like a portal. They have a lot of participating merchants and they will either apply the discount directly of give you a coupon code.
I haven’t had the time to look through all the merchants, but there is some gift card reselling opportunities here. I’ll update the post once I focus more on it. In the meantime let us know if you discover any of these opportunities.