GeoHotz is back again with another jailbreak for all idevices on iOS 4.1 is out at limera1n.com. It is still somewhat beta so it is advised to wait for new beta revision. Mixed reviews atm. This will work on every single iDevice out. That includes late bootrom ipod touch 2g (MC) (apperantly not yet), ipod touch 3g which have been tethered so far. All iDevices are untethered AFAIK.
EDIT: Beta 2 is now out with improved untether method.
Only supports:
"iPhone 3GS, iPod Touch 3G, iPad, iPhone 4, iPod Touch 4G
3GS new bootrom is broken, fix pending"
iPod Touch 2g (MC) doesnt seem to be supported quite yet