Sketch Repo - Collection of resources for anyone who uses Sketch
Sketch Talk - A community for Sketch users of all skill levels
Build with Sketch - Free LEGO-like kit for Sketch
SketchCasts - A weekly screencast, all about how to use Sketch
Icon Slate - Icon Slate lets you easily compose, import and export desktop icons in many formats.
Sketch 101 by Designlab - Learn Sketch in this free course w/ downloadable templates