today:
199 - HDNet & some PPV Movies - HDNet is sports HD Programming
509 - HD-HBO - HBO in HD {depends on programming} http://www.directv.com/DTVAPP/imagine/HDTV.jsp
no idea when others are coming. HD Showtime has been rumored for many months but nothing so far...
HDNet is well worth the price of the receiver for me
HDnet shows quite a bit more than sports. A lot of documentraies and an occasional movie (of varying print and content quality), along with MLB and NHL games and national broadcast NBA on NBC HD games are shown since they're actually produced by HDnet.
One of these days, you've gotta expect Showtime HD to show up too, since it already exists but isn't carried by DTV. The rumors run rampatant that a 3rd channel will be added fairly soon.
HBO-HD crops most films to 1.78:1 regardless of their OAR.