In 1982, the U.S. Supreme Court issued a decision, New York v. Ferber, which allowed the government to constitutionally ban the knowing distribution of even non-obscene "child pornography".
At issue in the case is whether the USPS may constitutionally ban petition circulators for collecting signatures while standing on post office sidewalks.
A Supreme Court argument today on whether a state may constitutionally ban the advertising of liquor prices presented an interesting mix of free-speech principles and economic theory.