I use the Moshi Mini Display port to HDMI adapter to connect to my external monitor (with HDMI) or to my flat screen with HDMI. It works very well and is available in the Apple store.
I had a 2009-MBA connected to an RCA HDMI tv via a miniDVI-to-HDMI connector. It worked perfectly.
I recently switched to a new MBA-2011 with thunderbolt and I read I could use the exact same connector. It works but:
a. the image if I recall correctly, seemed much better on my old MBA, which shouldn't be.
b. my screen on the tv is not sized correctly and doesn't fit. I can't see the left or right edges of my computer screen on the tv. Each side is about 10-20 pixels short.