This one I find so simple but so illuminating. A GIF from NikolayS that shows how a sewing machine makes a stitch.
Copyright Licence: Creative Commons Attribution-Share Alike 3.0 Unported.You can re-use this file so long as you say who created it and share it under the same licence.
Lee LeFever of CommonCraft is creating a guide on how to create GIFs to use as explainers. He blogged about it (which is where I found this sewing machine GIF) and you can sign up for the guide at explainergif.com.
He also wrote a nice post about the power of GIFs to explain as well as entertain: Welcome to the Next Golden Age of Animated GIFs.
That post includes a number of GIF-making tools including:
gifyoutube.com — Simply add “gif” to any YouTube URL (gifyoutube.com/…) to open this tool.
Imgur.com — The popular image hosting site recently rolled out a new GIF conversion tool that converts GIFs to smaller mp4 videos.
LiceCap — Free, works on Windows and OSX
Then there are the lovely GIFs created for the GIF It Up competition run by Digital NZ and the Digital Public Library of America. The winners are here and you can see more of the GIFs on the GIF It Up tumblr.