In 2009, Kodak stopped manufacturing Kodachrome after 74 years. This film was the best transparency film available, at any time during the years of film photography. Because of it's complex processing, it was sold with processing charges included and once shot, it had to be posted to a Kodak laboratory. In the USA, I believe things were a little different, but those of us in the rest of the world had to wait weeks to have our slides returned.
I always thought Kodachrome was made in 35mm only but I was wrong. Medium format and even 4x5 sheet film was manufactured, and if you click here you will see absolutely magnificent images taken during the Second World War which amply illustrate the quality that attracted professionals who could afford to wait weeks for results, such as National Geographic shooters.
It is also sad but inevitable that Kodak have just announced that they are ceasing to manufacture colour reversal (transparency, slide) film.