awwwards. - [Top websites] A showcase of all the best-designed websites (voted on by designers).
Behance - [Design showcase] A place where designers showcase their work. Filterable with categories for UI/UX projects.
dribbble - [Design showcase] Unique design inspiration, generally not from real applications.
Landings - [Web screenshots] Find the best landing pages for your design inspiration based on your preference.
Lapa Ninja - [Landing page / UI KIts / Web screenshots] Lapa Ninja is a gallery featuring the best 6025 landing page examples, free books for designers and free UI kits from around the web.
LovelyLanding.net - [Landing Page Designs] Frequently updated landing page screenshots. Includes Desktop, Tablet, and Mobile screenshots.
Mobbin - [Mobile screenshots] Save hours of UI & UX research with our library of 50,000+ fully searchable mobile app screenshots.
Uiland Design - [Mobile screenshots] Explore Mobile and Web UI Designs from Leading Companies in Africa and the world.
Mobile Patterns - [Mobile screenshots] A design inspirational library featuring the finest UI UX Patterns (iOS and Android) for designers, developers, and product makers to reference.
Page Flows - [Mobile / web videos and screenshots] Videos of full flows across many mobile and web apps. Also includes screenshots. Highly searchable and indexed.
Screenlane - [Mobile screenshots] Get inspired and keep up with the latest web & mobile app UI design trends. Filterable by pattern and app.
scrnshts - [Mobile screenshots] A hand-picked collection of the finest app store design screenshots.
Refero - [Web screenshots] Tagged and searchable collection of design references from great web applications.