M-x menu-bar-open, which is usually bound to F10. This works with and without menu-bar-mode (which just shows the names of the menus at the top of the screen).
It lets you execute menu commands from the keyboard, using completion:
ESC M-x
Menu command:
Menu command: t [TAB]
Menu command: Tools >
Menu command: Tools > Compa [TAB]
Menu command: Tools > Compare (Ediff) > Two F [TAB]
Menu command: Tools > Compare (Ediff) > Two Files... [RET]