Apple has just released the final GM (Gold Master) version of iOS 4.2 to developers! Only members enrolled in the iPhone Developer Standard or Enterprise Program can access these bits by signing into iOS Dev Center (aka Apple Developer Connection).
We will be back soon with change log for the final GM version (if any) of iOS 4.2. Stay tuned !!
Download iOS 4.2 GM for iPhone, iPad, iPod touch and SDK
UPDATE 1: Want to Jailbreak iOS 4.2 GM? Follow our complete step by step guide posted here to jailbreak iPhone 4, 3GS, 3G and iPod touch 4G / 3G / 2G on iOS 4.2 using Redsn0w.