Some Official Usability, User Experience & User Interface Guidelines
I know how these links are useful for me maybe should be useful for you too.
Apple
iPhone & iPad (iOS) User Experience Guidelines iPhone & iPad (iOS) User Interface Guidelines Mac OS X User Experience Guidelines Mac OS X User Interface Guidelines
BlackBerry
Blackberry Browser Content Design Guidelines (PDF) User Interface Guidelines for Blackberry Playbook Tablet User Interface Guidelines for Blackberry Smartphones
Android User Interface Guidelines Design Principles Google TV Web Site Optimization Resources Website Design & Content Guidelines
HP
User Interface Guidelines for Palm webOS Enyo Design Guidelines
IBM
Design Principles User experience guidelines for IBM Lotus rich client applications and plug-ins
Microsoft
Windows phone mobile UI Window 8 - Design UX for app.
Motorola
Motorola Best Practices for Android User Interface
Nokia
Design & User Experience Library Design Principles Hildon UI Style Guide Symbian Design Guidelines Usability & Design Resources User Experience Resources
Samsung
Samsung bada Application User Interface Guide
SonyEricsson
Reference: http://usabilitygeek.com/