The online coupon site Groupon has made big news lately, as it's membership has grown to 60 million worldwide, with half of those in North America.

They have a simple business model, where they post one deal a day , such as half off at a local cafe or a buy-one-get-one-free clothing deal, and visitors have 24 hours to sign up for the deal. Groupon's success has spawned numerous copycat sites, and while the formula they use is pretty much the same, the mix of bargains you will find from site to site can vary a lot. Groupon will sometimes offer deals at national chains, and offers the best variety of deals. Many of the deals are good for between 6 months and 1 year, and each deal needs a buy-in from a certain number of people to take effect. Because Groupon is so large, most deals do meet their buy-ins, and Groupon now even has apps for iPhone, Android and Blackberry.