1. Web
    Home of the Web Component polyfill and lots of great articles, discussions and best-practices.
  2. Google Custom Element Primer (v1)
    Primer for using the newer v1 of the custom element specification.
  3. Google Shadow DOM Primer (v1)
    Walkthrough of the newer v1 Shadow DOM specification.
  4. Polymer Project Documentation
    Hub for everything Polymer: documentation, toolboxes, element catalogsā€¦
  5. Polymer YouTube Polycasts
    Great series of short videos, each focusing on a particular Polymer feature.