iPhone Dev Team had released Redsn0w 0.9.6b2 to jailbreak iOS 4.1 for iPhone 4, iPhone 3GS, iPhone 3G, iPod Touch 4G, iPod Touch 3G, iPad and Apple TV 2G yesterday.
They have announced that the new version of Redsn0w can jailbreak iOS 4.2 GM that Apple had released to developers yesterday.