David-
As Mike has already asked, what are you currently using (what modules) by way of displaying content on your DNN site?  Text/HTML, articles, blogs, forums or third party modules?  Whatever solution you might eventually employ will heavily depend on what you use to post/present content.

Generic Solution
A free, generic "most-whatever" solution is detailed in my blog post here (with code and working example):

  Create a "Most-Commented Blogs" module
  http://www.eguanasolutions.com/DNN_Blog/EntryID/13.aspx
 

If you have your DNN sitelog enabled you can easily modify the example SQL to instead return "most-viewed pages", "most-viewed forum posts", etc.   The homepage of the linked site (above) employs three different working examples of this solution to provide clickable lists of "most-viewed blogs", "most-recently-posted blogs" and "most-commented blogs".  It's super easy to do (and free!)

Cheers!
-mamlin