Apple
iOS Human Interface Guidelines
http://developer.apple.com/library/ios/#documentation/userexperience/conceptual/mobilehig/Introduction/Introduction.html

iPad Human Interface Guidelines (自2011年已合并入iOS Human Interface Guidelines)
http://www.hung-truong.com/blog/wp-content/uploads/2010/06/iPadHIG.pdf
apple4.us上的中文翻译：http://apple4.us/ipad-hig-chinese

Apple Human Interface Guidelines
http://developer.apple.com/library/mac/#documentation/UserExperience/Conceptual/AppleHIGuidelines/XHIGIntro/XHIGIntro.html


Google
Android User Interface Guidelines
http://developer.android.com/guide/practices/ui_guidelines/index.html

Motorola’s Best Practices for Android UI
http://developer.motorola.com/docstools/library/Best_Practices_for_User_Interfaces/


Microsoft
Windows Touch UI Guideline
http://msdn.microsoft.com/en-us/library/cc872774.aspx

UI Design & Interaction Guide for Windows Phone 7
http://msdn.microsoft.com/en-us/library/ff637515(v=VS.92).aspx
http://download.microsoft.com/download/7/7/3/77371BBD-6613-4C1A-ACBF-08365C09D5FA/UI Design and Interaction Guide for Windows Phone 7 v2.0.pdf

UI Guidelines for Windows Mobile 6.5
http://msdn.microsoft.com/en-us/library/bb158602.aspx

Windows User Experience Interaction Guidelines
http://msdn.microsoft.com/en-us/library/aa511258.aspx


Yahoo
Yahoo UI Library
http://developer.yahoo.com/yui/


RIM
UI Guidelines for BlackBerry 6.0 Smartphones
http://docs.blackberry.com/en/developers/deliverables/17965/index.jsp?name=UI+Guidelines+-+BlackBerry+Smartphones6.0&language=English&userType=21&category=Java+Development+Guidelines&subCategory=

BlackBerry Browser Content Design Guidelines
http://docs.blackberry.com/en/developers/deliverables/4305/BlackBerry_Browser-4.6.0-US.pdf


Palm/HP
webOS UI Guidelines
http://developer.palm.com/index.PHP?option=com_content&view=article&id=1836


Nokia
Nokia Design & User Experience Library
http://library.forum.nokia.com/index.jsp?topic=/Design_and_User_Experience_Library/GUID-A8DF3EB8-E97C-4DA0-95F6-F464ECC995BC_cover.html
Forum Nokia Design Portal
http://www.forum.nokia.com/Design/

Hildon UI Guidelines for Nokia Maemo
http://www.forum.nokia.com/info/sw.nokia.com/id/eb8a68ba-6225-4d84-ba8f-a00e4a05ff6f/Hildon_2_2_UI_Style_Guide.html

MeeGo UI Design Guidelines
http://meego.com/developers/ui-design-guidelines/handset
http://www.forum.nokia.com/Devices/Maemo/Documentation/

Nokia Series 40 UI Style Guide
http://www.forum.nokia.com/info/sw.nokia.com/id/73e935fe-8b59-43b2-ab3e-1c5f763672db/Series_40_UI_Style_Guide.html
Symbian^3 UI Style Guidelines
http://www.forum.nokia.com/info/sw.nokia.com/id/5c419b14-75ff-4791-b1a8-db1e0d72e36e/Symbian_3_UI_Style_Guide.html


Misc
Bada Application UI Guide
http://dpimg.ospos.net/contents/docs/resources_1004/com.osp.appuiguide.help/html/FramesetMain.html?menu=MC01010403&mtb1=&mtb2=

Sony Ericsson UI Rulebook
http://developer.sonyericsson.com/cws/download/1/716/984/1262667210/DW-102212-UI_Rulebook.pdf

gnome ui guidelines
http://library.gnome.org/devel/hig-book/stable/

kde ui guidelines
http://developer.kde.org/documentation/standards/kde/style/basics/index.html
http://developer.kde.org/documentation/design/ui/

eclipse ui guidelines
http://www.eclipse.org/articles/Article-UI-Guidelines/Index.html