Thanks to pod2g and all his hard work, an untethered jailbreak is now available for the original iPad, iPhone 4, iPod touch 4, and older models. Both redsn0w and Corona have been updated to support the new, untethered jailbreak.
A few days ago, @pod2g gave the untether to both the iPhone devteam and the chronic devteam. We’ve put it into redsn0w 0.9.10 and PwnageTool, and the chronic devteam put it into a Cydia package (the same set of exploits is in all three).