[Powerlord]

I wrote a SourceMod Menu Generator a while back. Although there's a second version that is a bit more streamlined.

Having said that, plugins can add themselves to the admin menu using things found in adminmenu.inc and topmenus.inc. It's a bit more complicated than a normal menu, but TopMenus are smarter than traditional menus are... items you create in them have associated admin permissions, for example.