Kanex XD has announced the Kanex iAdapt HDMI V2 (http://kanexlive.com/products/iAdaptV2.html), an US$34.95Mini DisplayPort to HDMI adapter that supports audio for the newer Macs.
The iAdapt HDMI V2 has been engineered to support full 1080p HD video output and audio to a single HDMI cable. Kanex iAdapt HDMI V2 will allow you to connect a Mini DisplayPort equipped Apple computer to any HDMI enabled external display such as an HD projector, monitor, or HDTV.  

It supports audio and video passthrough for April 2010 MacBooks and MacBook Pros and all 21.5-inch and 27-inch iMac desktop computers. The iAdapt HDMI V2 will be released later this summer.