In my project I add reference on the WPFToolkit assembly, restart Visual Studio and has not seen WPFToolkit components in my VS ToolBox window. What I do wrong?
Toolbox doesn't automatically pick up components/controls in referenced assemblies. It does however automatically pick up components/controls that are built in your projects.
You can right click the toolbox and choose "Customize" and you will get a dialog that lets you browse to the assembly and check off any controls that you want to appear. It might be helpful to create a new tab in the toolbox first.