watch the BBC series Planet Earth available on HD-DVD.
[Link: cbc.ca]not only is it a VERY interesting documentary but the filming is nothing short of AMAZING. i have never seen such beautiful scenery and my life, tonnes of aerial and satellite footage - and all in HD glory!!
even if you hate documentaries, there is no better way to show off your HDTV's ability... the scenery is so awesome you could have it running as background while you listen to music or whatever.
i know this title has been discussed somewhere here in the past, but i had to throw my recommendation in, as i was simply blown away by the first few episodes (i believe there are 11 or 12 episodes all together on 4 discs).