The just released limera1n promises to jailbreak iOS 4.0-4.1 on iPhone 4, iPhone 3GS, iPad, iPod Touch 4G, and iPod Touch 3G. It's Windows only for now, with Mac & Linux support coming soon.
Jailbreak at your own risk! Limera1n is a different jailbreak tool than the GreenPois0n jailbreak tool we were expecting to release tomorrow. [limera1n]