DirecTV:
HBO HD - 24 hours a day
Demo channel/PPV - Demo during business hours so stores can use this channel and PPV late in the evening.
Dish Network:
HBO HD - 24 hours
Showtime HD - 24 hours
PPV - 24 hours
Demo channel - 24 hours
Dish requires the model 5000 with HD demodulator. These have been discontinued but have become popular again with the ability to record HD material on a PC. The current model is the 6000. Decodes satellite HD and OTA HD (with an optional module) and outputs 1080i and 720p.
DirecTV has multiple models from all the major manufacturers. They all decode satellite and OTA HD. I think that they only output 1080i though.
RCA DTC-100 - cheapest and been around the longest.
Sony HD100 - very new. Has some problems with sub-channels on OTA broadcasts.
Hughs/Mitsubishi/Toshiba - new. No major problems.
Check out
www.dbsforums.com and
www.avsforums.com for satellite info and HDTV info respectively.