This website provides patterns for various pages and features you would need for an app.
This website is a digital mood-board that displays artworks, photographs and other images posted by designers all over the world. (also known as inspiration.)
A database for fonts, web and print compatible with licensing.
4/ UI Patterns
Another database for UX design patterns, this one goes into more detail about particular application design features.
5/ IOS Patterns
Another database for iPhone interface patterns
This is an app/website that allows the user to upload sketch wireframes to create an interactive prototype.
A website that allows the user to turn wireframes into an interactive application prototype.
Similar to Pinterest, Behance is a database that allows the public to view works by designers but also upload their own.