SmartDraw - Instead of starting with a blank screen, SmartDraw gives you the exact template you need.
Invision - Prototyping and collaboration for design teams
Creately - The new interface for work to ideate, plan, and execute
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
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.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project