Here is the video tutorial for Jailbreak your iPhone, iPod Touch, or iPad on iOS 4.2.1 using GreenPois0n RC5. Head-over to the next page to watch the video.
This is an UNTETHERED Jailbreak for all iDevices (iPod Touch 2G, iPod Touch 3G, iPod Touch 4G, iPhone 3G, iPhone 3GS, iPhone 4 and iPad). Download GreenPois0n utility for Windows, Mac, Linux from here
[Thanks to dahacker13]