ASP.NET version of Joomla [closed]
I've been told by a friend that Umbraco is everything you would ever want in a CMS (and it was in the list that Nathan included in his answer). This recommendation is coming from a guy who's built several CMS solutions over the years and after taking a brief look at it, I think I'm going to try to push my clients towards using it over their current solutions.
DotNetNuke is quick to set up and get running. It is the best ASP.NET CMS that I have used.
It comes with many modules, and can be extended with numerous commercial and free 3rd party modules.
It is very easy to change to look of a DNN site by simply changing the assigned skin, and many 3rd party skins are available as well.
Warbeats.com runs on DNN, and handles quite a bit of traffic.