I've used DotNetNuke and its a very good system but to get the fun stuff you need to buy the commercial add-ons which is not always a good idea as DNN do very regular upgrades and the third-party stuff always lags several version behind.
You can easily run multiple sites off a single installation of DNN and the free stuuf should be more than enuff to give you a fairly robust out-of-box solution.
The source code is written in VB - not sure if they do a C# version
I have not seen this asp.net CMS before but it seems that is a cutting edge technology. It seems truly complete all in one asp.net cms application that has 30+ built in modules. They also provide you data services so you can access your website content, stores leads, campaign data anytime, anywhere. Company has also provide asp.net ecommerce solutions.
We use Contensis at my place of work but I wouldn't recommend it at all. It crashes a lot, doesn't work properly in any browser other than IE and sometimes screws up CSS classes. For example: I would set an image to the previously defined "imageleft" to make it float to the left but when I edit the page a bit, it decides to also add the class "sys_clear" to the image for some unknown reason. A class which doesn't exist which wouldn't normally cause a problem but it doesn't put a space between the classes so in the code it looks like class="imageleftsys_clear" meaning it's trying to call a non existent class.