U.S. STATE LAW #
Psilocybin mushrooms are illegal in every state in the United States except Florida (see below).
Specific state laws can be accessed through this state-by-state list. An Overview of case law for several states can be accessed here.

Psilocybin Mushroom spores are legal to possess in every state except California, Georgia, and Idaho. (see details).

Florida #
Florida stands out because of a decision in 1978 in Fiske v Florida by the Florida Supreme Court which ruled that wild-picked psilocybin mushrooms could not be legally considered "containers" of psilocybin and thus would have to be specifically listed in Florida law by the legislature if they meant to make them illegal. Since the Florida legislature has not chosen to change the laws since then, wild Psilocybin mushrooms are presumptively legal to possess in Florida. This does not mean police won't arrest people for possession of even wild mushrooms, but this has been used as a successful defense against such charges.
New Mexico #
New Mexico appeals court ruled on June 14, 2005, that growing psilocybin mushrooms for personal consumption could not be considered "manufacturing a controlled substance" under state law. See Opinion: State of New Mexico vs. David Ray Pratt - June 14 2005