What started a short list became quite a big description, more details inside the post.
Image Cutter - javascript plug-in flexible, cross-browser friendly, touch friendly and has no dependencies.
ParsleyJS - declarative form validation JavaScript library.
Promise nuggets a github-book by @spion with good explanation and examples for Promises usage. Mostly on Promises alternative to async callbacks approach.
Bluebird - javascript promises library aimed to be almost "as fast as regular callback code" (and 100/10 times faster then Q and when). Worth to try out.
I was waiting for it so long :) Videoconverter.js - FFmpeg converted in JavaScript via Emscripten. It works in client browser, really works. It does not support x264 codec yet, but could be useful to create a video preview on client side etc.