I have these channels in High Definition on DirecTV (the current industry HD leader):
Discovery Channel, Animal Planet, National Geographic, Biography Channel, History Channel, Science Channel, A&E, BET, TNT, TBS, USA, Spike, Bravo, Sci-Fi, FX, MGM, Nickelodeon, Disney, Food Network, Cartoon Network, The Weather Channel, CNN, CNBC, ESPN, Country Music Television, MTV, Golf, HGTV, Universal HD, HDNet Movies, etc.
Not to mention the ~25 HD sports channels and HBO, Showtime, Movie Channel, Starz, etc. premium movie channels.