Banned in the U.S.

The Telecommunications Act of 1996 banned "indecency" on the Internet and rendered many sites technically illegal until the provisions were ruled unconstitutional in 1997.

Here is a list of things on the Internet that the U.S. government made it illegal for you to see:

All the above would be legal for you to see if they were put on paper. The U.S. Congress passed a law (later overturned) making them illegal in electronic form.