Mobile & multi-device lessons learned: free iBook by Luke Wroblewski
8 PSD files, over 50 templates, and hundreds of components, this UI kit has any design element you need to create beautiful iPhone interfaces.
Interesting article on Design Process over at GOV.UK
The transition from skeuomorphism to flat design is old news. However, skeuomorphic motion is great usability.
Google Material’s new style and principles in action: http://www.polymer-project.org/apps/topeka/