Invision - Prototyping and collaboration for design teams
Mobbin - Latest mobile design patterns & elements library
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
pttrns - iPhone and iPad user interface patterns
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
Page Flows - User flow design inspiration for mobile & desktop