SmartDraw - Instead of starting with a blank screen, SmartDraw gives you the exact template you need.
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.
Creately - The new interface for work to ideate, plan, and execute
draw.io - Online diagramming application
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
Sketch - Professional digital design for Mac.