Earlier this month, Comex of Spirit and JailbreakMe fame confirmed that a more efficient userland-based untethered jailbreak method for iOS 4.2.1 will be released before Christmas 2010.

And now, MuscleNerd of iPhone Dev-Team has given further confirmation that a untethered jailbreak solution for iOS 4.2.1 is indeed in works, and that it will be ready for prime-time use somewhere around Christmas.

scotty6kids78: @MuscleNerd are we any closer to the unteathered #jailbreak for the new #ios4.2 on #iphone4 ?
MuscleNerd: @scotty6kids78 it’ll be here by Xmas (not because we’re sitting waiting for Xmas, but because it’s achievable deadline)

This untethered solution will almost certainly be applicable to all current iOS 4.2.1 devices, including the new A4-based ones which includes iPhone 4, iPad, Apple TV 2G and iPod touch 4G.
More info on this as it comes, stay tuned for that !