User Inyerface - A painful illustration of bad UX
Really Good UX - A library of screenshots for UX inspiration
Befront - Learn UX/UI design skills in practice with bite-sized tasks
Usability.gov - Resource for user experience (UX) best practices & guides
Frontend Mentor - Supercharge your front-end skills by building in a real-life workflow. Solve real-world HTML, CSS and JavaScript challenges whilst working to professional quality designs.
UX Check - Easy heuristic evaluations on your website (chrome ext.)