The online deals space is certainly heating up as more and more marketers get in the game. The decision for many is whether they want to build their own version of a deals site or whether they want to use one of the big names in the space.
For the most part, the biggest name in the space is Groupon. They are in the news constantly for a variety of reasons which are a mix of good (tremendous growth) and bad (poor executive decisions about marketing etc) but they are the de facto industry leader.
Unlike the search marketing game though Groupon’s position is less than bulletproof since the ability to copy the process isn’t a high barrier to entry. What is tough is scale and that’s where Groupon has the edge over most little guys.