Really Good UX - A library of screenshots for UX inspiration
Usability.gov - Resource for user experience (UX) best practices & guides
Startup Timelines - How the frontpages of famous startups changed over time
UX Check - Easy heuristic evaluations on your website (chrome ext.)
UXTesting - Discover how your mobile users feel
Heurix.io - Heurix is a free heuristic evaluation tool that helps you work out how to improve your website.