Unsolved Mysteries
I'm a big fan of this Robert Stack hosted series, that was quite similar in tone,subject matter, and quality.
Some episodes featured cases that had been on "In Search Of..." like:
Amelia Earhart, King Tut, the lost Dutchman mine, UFO Australia, shroud of Turin, among others.
Here is a link for those interested:
http://unsolvedmysteries.wikia.com/wiki/Unsolved_Mysteries_Wiki