If you have a Mac that was introduced from mid-2010 on and it has a Mini DisplayPort, Kanex has a couple of solutions that can turn your HDTV or other HDMI-equipped video device into a monitor with full audio pass-through.
I recently had a chance to test out two such solutions from Kanex. The first is the US$29.95 Kanex iAdapt V2, which is an adapter that plugs into the Mini DisplayPort and has an HDMI port on the other end. It's useful if you already have an HDMI cable and just want to be able to plug it into your compatible Mac. The second is the $44.95 Kanex Mini DisplayPort to HDMI cable, which combines the adapter with a 10-foot long HDMI cable. You plug one end into your Mac, the other into your HDTV.
For compatible devices, which include the MacBook (Late 2010 release), MacBook Pro 13 /15 /17 inch (Mid 2010 release), iMac 21.5/27 inch (Early 2010 release), MacBook Air 11 /13 inch (Mid 2010 release) and Mac mini and Mac Pro (Mid 2010 release), you not only get a selection of HD video formats (720p / 1080i / 1080p), but also 5.1 surround sound pass-through. This could be extremely useful for business travelers who want to look at presentations or videos on a screen that's bigger than the one on the 11.6" MacBook Air -- they can turn to the large flat-panel HDTVs that are now in many hotel rooms.
I tried out both the cable and the adapter with my little MacBook Air on one end and a 52" HDTV on the other, and it worked fine. The cable and adapter have an auto-EDID feature that automatically matched the maximum resolution of my display, so my MacBook Air started pumping out 720p video immediately. The only negative, and it might be due to the HDTV I own, is that the Mac OS X menu bar was slightly cut off at the top of the screen.
Using System Preferences > Displays, I was able to switch the display resolution to 1080i, 1080p and several other resolutions that were non-standard for the HDTV. Most of them looked great on the big screen. I was initially unable to get sound working until I used System Preferences > Sound and noticed the HDTV was showing up as a sound output source, then selected it. The sound quality was excellent through the HDTV; however, I usually send audio to a home theater unit that is connected to the system.
If you're looking for a way to send just video from your Mac to an HDMI-equipped monitor, projector or HDTV, there are many less expensive adapters that are available from sources such as Monoprice. However, the Kanex adapter and cable both provide the audio-out capability that most of those cheap cables lack, and if your Mac is new enough to support HDMI audio, this is a wonderful way to get it all in one solid cable or adapter.