Host your own WPF Designer
Last week I had to find a WPF Designer which can be hosted in a .Net application, the result of my brief research was Aurora XAML Designer. As far as I sow it isn't possible to host cider (VS WPF Designer) in your own application so lucky for me I found a reasonably good alternative in Aurora XAML Designer.
I've contacted Patrick from Mobiform and he was kind to send me a Trail Version for me to test. The result looks quite promising when I was able to easily take control of different parts of the designer such as manipulate the Toolbox create Tool-bars Pans and so on. Eventually it seems like a nice solution if you want to enable the end user to edit / create simple WPF forms from your application without having to install Visual Studio or Expression Blend.
Here are some pictures of my own self hosted Aurora XAML Designer:

