Or facebook...I still haven't figured out why facebook hasn't stepped into this space yet. They have the distribution, they just need the marketers in select regions.
Facebook Places:
http://www.facebook.com/places/
http://news.ycombinator.com/item?id=1616082
Facebook Deals:
http://www.facebook.com/blog.php?post=446183422130
http://news.ycombinator.com/item?id=1865817
EDIT: Updated style.
Agreed, they have a huge distribution channel but so does for instance Target or Walmart, but groupon just doesnt align to those companies core competencies. Hence not a great fit.