Alt+Tab to desktop
I wonder why no windows manager or desktop environment implements this. I guess they are too busy copying Microsoft Windows to invent anything original. Anyway, the basic idea is that, instead of having a special Show Desktop button, we would always have the Desktop listed when switching windows or running applications.
This way you can easily go to Desktop by using keyboard, and not have a special shortcut for that (not to mention that possibility of shortcuts is not something most users are even aware of)