Laws of UX - Key maxims that designers must consider when building UX
Invision - Prototyping and collaboration for design teams
Design Principles - An open source repository of design principles and methods
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Product Disrupt - A design student's list of resources to learn Product Design
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.