Hard science and world-renown experts...
The Universe (History Channel)
Chock full of great topics with experts like Neil Degrasse, director of the Hayden Planetarium at the Museum of Natural History / Rose Space Center in NYC.
Speaking of Dr. Degrasse, he hosts PBS's most venerable, and longest-running science program. Never disappointing and Dr. D is probably one of the most enigmatic hosts since the late Dr. Sagan.
How the Earth Was Made (History Channel)
Another wonderful show focusing on more than geology or volcanology but really a whole slew of Earth sciences (meteorology, oceanography, biology, thermo-dynamics, etc.). My favorite so far has been the recent episode on Iceland (timely!) which described the birth of the island of Surtsey in 1963, off the southern coast. An island the literally "arrived" via volcanic gestation.
Into the Universe with Stephen Hawking (Discovery Channel)
Arguably the smartest man in the (known) universe, Dr. Hawking has made quite a splash in recent episodes of his program about extra-terrestrials and the search for life in the universe. Into the Universe is a fantastic program that gives the topic of cosmology the beauty, grace, and raw intellect it so much deserves.
Planet Earth (Discovery Channel / BBC)
One of my all-time favorite programs. I own the DVD and it's spectacular documentation of the natural world at this time in history is superb. It sets a new standard in TV documentaries not only in cinematography but in scope--covering every continent and type of environment the planet has to offer. From Wikipedia:
To capture all the footage required by the producers, 71 cameramen and women filmed in 204 locations in 62 countries on all seven continents, spending more than 2000 days in the fieldIf there is any program here you must see, this is the one. A sequel series Life is now airing on Discovery in the US.
Speculative, but still credible...
Life After People (History Channel)
By now you've likely figured that I watch too much History Channel, and while I can't completely deny that, most of these episodes I caught on On-Demand. This program takes current pop-culture's post-apocalyptic fascination and tries to visualize for the viewer what a post-people world would look like months, years, centuries, and millennia after we're long gone. A really intriguing topic with plenty of credible experts in the Earth sciences as well as metallurgists and investigative experts.
Cities of the Underworld (History Channel)
This is another great show that's filled with plenty of factual and historical background on underground hideouts, lairs, tunnels, and more, hosted by actor Dan Wildman. I've put it into "speculative" if only because many of the wonderful stories are often based on a combination of myths and local legends--to be fair though an expert archeologist is always featured. The show was recently discontinued on the History Channel, but I'm certain it will pop up (if it hasn't already) on DVD soon.
Hardly credible, fun as hell...
Ancient Aliens (History Channel)
This show wanders dutiful (and happily, I might add!) into science fiction territory, but it's filled with so many great ideas--and so well constructed that it's impossible not to watch. My only regret is that the network's current audience may take much of this for fact. Frankly, I've gone to bed paranoid a few times already! ;)
Honorable mention...Sci Fi Science: Physics of the Impossible (Science Channel)
I've only watched an episode or two online since we don't dropped the Science Channel from our subscription package (I still miss it...) but Sci Fi Science has a lot to appreciate in the way of using the hard sciences to explain how science fiction concepts could work. File this under "speculative" if you need to put it on the spectrum. It's hosted by Dr. Michio Kaku one of the world's leading astro-physicists and author of one of my favorite cosmology books, Parallel Worlds: A Journey Through Creation, Higher Dimensions, and the Future of the Cosmos. He's the Science Channel's default host for many of their mainline shows, including a series that previously aired on the topic of his book.
Ancient Monster Hunters (History Channel)
One of my favorite single-episode docs that traces the origins of the mythological beasts such as the cyclopes, and griffins in antiquity as told through the paleontologists, archeologists, geologists, and biologists who've done the dirty work. The griffin segment is particular fascinating. It airs occasionally, but your best bet is to monster-hunt a copy down.
This is just a sampling of what's out there to gorge your eyeballs on. I'm a big fan of ancient history (particularly Egyptian) as well as paleontology--and there's just too many to name, including many one-off specials--but hopefully this list gets you started. So, what are your favorite documentary programs to pull ideas from for stories, games, or whatever gets your gears turning?
Let us know in the comments!