The Game UI Database contains a large library of UI's used within games across many genres. Useful for finding inspiration for your own game or project.
Topics
UMG Layout Techniques for Unreal Engine
Fast Render Target Rendering in Unreal Engine
Making UIs With C++ in Unreal Engine
Textures for VFX - Database
UMG Slate Compendium
Professional Game Development in C++ and Unreal Engine