Is there a good GUI designer (read: drag 'n drop/WYSIWYG) for the plain old Windows API? I'm not looking for something that uses Qt, GTK, .NET, etc, just plain old Windows API.
Must be usable with either C or C++.
You are looking for a resource editor. Visual Studio Professional, Premium and Ultimate have one built into the IDE. You can access it by creating a new .rc file and then adding a resource to it.
If you're not using Visual Studio you can use an external resource editor such as ResEdit. Not having it built into the IDE is a little bit more of a hassle unfortunately.