This ever-growing curated collection of interface patterns on CodePen is a reliable source of inspiration.
This is witchcraft. I’ve been deconstructing the CSS to figure out how this works and it’s really clever.
(Hint: try commenting out some of the CSS and see what happens.)
A lovely little selection of loading indicators powered by CSS animations and transitions.
Want to indicate that something is happening on a web page, like... oh, I don't know... an Ajax request or something? Here's a cornucopia of animated progress indicators.