I am in process of writing a C# Windows Forms application using Visual Studio Express 2010 ENU SP1. Further VS specifics are at the bottom of this post. I recently made so
Although this is quite an old thread, I want to share my case and the solution.
I had the same problem but I used Telerik WinForms component for my Form. I couldn't see the designer until I realize that the design-time capabilities of RadControls for WinForms are implemented in the Telerik.WinControls.UI.Design.dll assembly. Then I add the reference and now the designer shows up.