Canon has released the Macro Ring Lite MR-14EX II. In Canon’s press release, the new light is mentioned as being compatible with the 600EX-RT; however, that compatibility apparently does not extend to the radio transmitter compatibility.
The biggest changes appear to be increased brightness from new LEDs for low-light focusing and the ability to control the ring light’s settings from the menu system of compatible DSLRs. Additionally, the left and right flash tubes can be controlled independently.
The Macro Ring Lite MR-14EX II retails for $549 and is currently available for pre-order. Check it out here at B&H Photo.