A powerful control package (for Ria) is recommended)

Goa winforms contains the main content of system. Windows. Forms, allowing you to develop Silverlight RIA (Silverlight 1.1) and flash applications in Microsoft Visual Studio. Program (Use Vs + C # To develop flash)

Goa winforms supports more than 40Controls and components:

• Control, containercontrol, scrollablecontrol, panel
• Button, checkbox, radiobutton, groupbox, label
• Textbox, numericupdown
• Imagebox, imagelist
• Scrollbar, hscrollbar, vscrollbar
• Form, MessageBox, cursor
• ListBox, checkedlistbox
• ComboBox
• Treeview
• Monthcalendar
• Tabcontrol, Splitter
• Tooltip, progressbar, Timer
• Toolstrip, statusstrip, menustrip, toolstripbutton, toolstripcombobox, toolstripdropdown, toolstriplabel, toolstripprogressbar, toolstripseparator, toolstripsplitbutton, toolstriptextbox
• Xamlcanvas (Silverlight specific)

The development method is similar to the Development of winform. below is the main Code : Public   Class Myform: system. Windows. Forms. Form
{
Private Button button1;
Private Label label1;
Private System. componentmodel. Container Components =   Null ;

Public Myform ()
{
Initializecomponent ();
}

Protected   Override   Void Dispose ( Bool Disposing)
{
If (Disposing)
{
If (Components ! =   Null )
{
Components. Dispose ();
}
}
Base . Dispose (disposing );
}

Private   Void Initializecomponent ()
{
This . Button1 =   New System. Windows. Forms. Button ();
This . Label1 =   New System. Windows. Forms. Label ();

This . Suspendlayout ();

This . Button1.location =   New System. Drawing. Point ( 84 , 140 );
This . Button1.name =   " Button1 " ;
This . Button1.size =   New System. Drawing. Size ( 104 , 36 );
This . Button1.text =   " Click me " ;

This . Label1.location =   New System. Drawing. Point ( 40 , 44 );
This . Label1.name =   " Label1 " ;
This . Label1.size =   New System. Drawing. Size ( 200 , 44 );

This . Controls. Add ( This . Label1 );
This . Controls. Add ( This . Button1 );

This . Resumelayout ( False );
}

Public   Static   Void Main ()
{
Application. Run (NewMyform ());
}  
}

Note: Goa winforms is free of charge. Goa winforms professional is charged and contains more than 30 Extension controls.
it's great to write Silverlight and flash using winform.
there is another similar thing: http://www.codeplex.com/visualwebgui. it is too slow to develop webin the form of winform.