In the 1940s, Superman cartoons were created by Fleischer Studios and Famous Studios. They are in the public domain, so they are free to download and watch (although DVD releases have been made). Links to all the episodes are on Wikipedia.
Since the episodes were released in the 1940s, the cartoons are racially insensitive, to put it mildly. This doesn’t factor into most of the episodes, but the episode “Japoteurs” has a very negative portrayal of the Japanese. Keep in mind that the episode was released less than a year after the bombing of Pearl Harbor, and you can understand the reasoning behind the portrayal (even if it’s obviously racist when you watch it today).
I would recommend watching them if you get the chance. In spite of their flaws, the animation quality is surprisingly good and it’s one of the first superhero cartoons. Besides, the price is right.