Product review (5 stars): For neat & tidy electrical boxes
I love these things.  They make boxes much more organized and allow quicker, easier changes (say when swapping out a switch, outlet, etc).  At first, I was a little skeptical of their holding power, but it's amazing how securely they grip the wire.

I'd really like to try Wago's newer lever nut design, as it's a little smaller and has a clear body so that you can visually check that the wires are fully inserted.  The levers are supposedly a little easier to use, as well.  Unfortunately, they don't seem to be readily available yet in the U.S.