Visio - Simplify and communicate complex information using data-linked diagrams.
draw.io - Online diagramming application
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.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
PathVisio - Open-source and free pathway analysis and pathway drawing software. Allows drawing, editing and analysis of biological pathways.
MyDraw - MyDraw is a powerful yet easy to use software for creating diagrams.