Long before Ancient Aliens, The X-Files, and pretty much any other TV show that dealt with the paranormal, there was In Search Of...

In Search Of... originated as a series of documentary specials hosted by Rod Serling (In Search Of Ancient Astronauts was the first) in 1973. The show became a regular series in 1977, hosted by Leonard Nimoy, and ran until 1982.

It was pretty goofy, with each episode opening with the following CYA disclaimer:
"This series presents information based in part on theory and conjecture. The producer's purpose is to suggest some possible explanations, but not necessarily the only ones, to the mysteries we will examine." In Search Of... tackled all the biggies, from Bigfoot to the Bermuda Triangle.

A good chunk of the episodes are now available on Youtube.