Previewed at WWDC, launching in the fall.
Secret 4G iPod Features?
It describes the new features including battery life improvements and the new click wheel... but offers a surprising hint at more to come:
But you should know that internally the new iPod is a ground-up reconstruction, and its really compelling applications the ones that very well might get the goat of anyone unable or unwilling to upgrade are still secret. All that Apple is saying is that there's more to this than what's being publicized.