Invision - Prototyping and collaboration for design teams
Atomic - The fastest way to design beautiful interactions
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
Pixelapse - Visual version control and collaboration workflow for open source and private design projects.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
pttrns - iPhone and iPad user interface patterns