Google Developer Kits
http://code.google.com/
Yahoo Developer Kits
http://developer.yahoo.com/download/
Windows Mobile Developer kits
http://developer.windowsmobile.com/
Bing SDK
http://www.bing.com/developer
http://msdn.microsoft.com/en-us/library/bb429619.aspx
Apple Developer Kits
http://developer.apple.com/sdk/
iphone sdk
http://developer.apple.com/iphone/
Android Developer
http://developer.android.com/sdk/
Symbian Developer kit
http://developer.symbian.com/main/tools_and_sdks/sdks/
Nokia Development kit
http://www.forum.nokia.com/Tools_Docs_and_Code/Tools/
Windows SDK
http://msdn.microsoft.com/en-us/windows/bb980924.aspx
Blackberry SDK
http://www.blackberry.com/developers/
Broadcom sdk (for bluetooth)
http://www.broadcom.com/support/bluetooth/sdk.php
... give more links!!
