All assemblies in the bin folder should be scanned on startup so the problem is not that you have your plugin in a separate assembly.
Have you decorated your class with the GUIPlugin attribute and selected a plugin area and supplied the path to your aspx/ascx?
Yes, I have done both. This is my plugin attribute:
DisplayName = "My GUI Plugin",
Description = "My GUI Plugin",
Area = PlugInArea.AdminMenu,
Url = "~/GUIPlugins/MyNewForm.aspx")
I even copied one of our existing plugins, and changed the relevant parts, and although it worked when navigated to, it didn't show in any menu, so I'm really stumped.
It seemed this was down to the initial project not being set up correctly. It now works as expected.
Anyone heard any news of the VS2010 template pack being released?