Really Good UX - A library of screenshots for UX inspiration
Usability.gov - Resource for user experience (UX) best practices & guides
UsabilitySquare - Get unbiased, instant feedback how to optimize your design.
UX Check - Easy heuristic evaluations on your website (chrome ext.)
Digital Psychology - Elevate your product using psychological techniques
Heurix.io - Heurix is a free heuristic evaluation tool that helps you work out how to improve your website.