Very useful collection of UI design guidelines for popular mobile and tablet devices.
Official user interface (UI) and user experience (UX) guidelines from the manufacturers, links to which you can find below, are a source of inspiration for mobile web and app design. Here, you will find guidelines, samples, tips, and descriptions of common mistakes. Many of the guidelines focus on native application development, but we can apply most parts of them to mobile web design too.
http://www.mobilexweb.com/blog/ui-guidelines-mobile-tablet-design