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

Google

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

User Interface Rulebook 

Reference: http://usabilitygeek.com/