The PocketWizard Plus IV is in stock and now shipping. For those not familiar with the new Plus IV, it essentially takes all the functionality of the Plus III and added a top shoe for mounting speedlights.
Additionally, the Plus IV will pass through TTL data when mounted on camera but limits transmission to manual triggering only.
The Plus IV is a transceiver, so each unit can serve in a transmitter or receiver role. It is compatible with most Canon, Nikon and Panasonic cameras. It also works with many Fuji, Olympus and Sony models or manual triggering. It will communicate with the older Plus III models as well for tying together speedlight and studio flash commingled setups.
Check it out here at B&H Photo.