Really Good UX - A library of screenshots for UX inspiration
Usability.gov - Resource for user experience (UX) best practices & guides
Laws of UX - Key maxims that designers must consider when building UX
UX Check - Easy heuristic evaluations on your website (chrome ext.)
Owletter - Keep an Eye on Your Competitors' Newsletters
Heurix.io - Heurix is a free heuristic evaluation tool that helps you work out how to improve your website.