I’m currently building my favourite CMS 
Drupal is a great open source CMS with tons of Modules/Templates and good support though to be fair to faster, true customization of it requires an advanced degree in hyperbolic topography
f Joomla in it’s stupid a (and its little dog Mambo too).
Plone is extremely robust, but an f’ing b to setup.
CMS Made Simple is good but not great, ++ uses Smarty and has on server Smarty/CSS editing so customizing the look and feel from one of the crappy templates is pretty easy.
Wordpress is good, but not really a CMS; plus it’s too easy…so easy that anyone can “make a website” and help ruin the Internet with the ridiculous $h!t that’s in their brains. I know I have…
sorry if I made pee-pee on anyone’s cheerios.
BTW w!sh, if you are going to make an incredibly complex CMS using ASP.NET, look into not doing that. Use CakePHP, RoR or another more responsive (and open source) framework, you and your users will appreciate it.
