draw.io - Online diagramming application
UI Garage - Specific mobile and web design patterns for your inspiration
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Muzli - UI/UX and Design Inspiration Chrome Extension
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Design Hunt - Curated design inspiration for everyone