Anything science, maths, medical, archaeology, anthropology, nature, history (especially British), genealogy, anything about the human body and human mind, .......
They're usually presented by people such as Marcus Du Sautoy, Brian Cox, Michael Mosely, David Attenborough etc.
Some favourites -
The Story of Science (Michael Mosely)
The Story of Maths (Marcus Du Sautoy)
Time Team (Tony Robinson)
Blood and Guts-The History of Surgery (5 part series) (Michael Mosely)
Medical Mavericks (4 part series about the researchers/doctors who experimented on themselves and changed the course of medicine in anaesthesia, vaccines, diet and disease, infection) (Michael Mosely)
Homo Futurus (doco about how the human skull shape has changed and why, and what they predict we'll look like in the future)
Some of Brian Cox's - Can We Make A Star On Earth, What Time Is It, What On Earth Is Wrong With Gravity, Wonders of the Solar System
Other - The Human Family Tree, Skin Deep, The Secret Life of your Body Clock, Did Cooking Make Us Human
So many more........................