I have been look around for Free/Open Source ASP.NET CMS / Portal systems for a while now, and have seived it down to two different ones.
Umbraco - http://umbraco.org
I tried Umbraco and it is not for the timid. I feel I'm a fairly technical person, Sr. Web Developer... and after several hours I gave up.
MojoPortal just works.
It has its flaws, but the simple fact that it just works means it wins.