Groupon started out doing deal-a-day coupons and did a ton of business, but as that model has begun to fade a bit, they have gotten creative and been exploring other verticals. They now are a fantastic source for all sorts of business related information and have come to be kind of like a yellow pages 2.0.
What’s especially cool about Groupon now is that they have integrated their cost saving coupons and vouchers into their business listings so you not only find what you’re looking for, but you also save some cash in the process. You can check out an example here for Denver tanning salons.