A favorite implementation of mine was 4dwm on SGI. You could middle-click on the trough and it would go directly there, rather than the normal paging by left-click. Still try to use it everywhere and am disappointed.
On Windows you get the same functionality with Shift+Left Click. You also get to see which applications use Qt since it isn't implemented there :-P.
Another great one is to lower the window to the bottom on middle-click of the title bar—excellent.
I seem to be able to get all these with Ubuntu Mate, but I'm not sure which toolkits fully support it and which don't.