greenpois0n untethered jailbreak for iOS 4.2.1, but unlike the build released 48 hours ago, this one's meant for Wintel boxes. The team's site seems to be down at the moment (shocker!), but there's a download mirror linked below if you just can't wait to get going. As always, we'd caution you to back up your iPad, iPod touch or iPhone before doing the deed, and since it's the first of its kind (for this version of iOS, anyway), we'd be ready to see a few bugs along the way. Minor details, we know.
[Thanks to everyone who sent this in]