US Postal Service: Chain Letters - Describes illegality of chain letters. - http://www.usps.com/websites/depart/inspect/fraud/chainlet.htm
Chain Letters Are Not Legal - Postal Service judicial decision that debunks the claim that sending a "report" in exchange for cash makes a chain letter legal. - http://www.usps.com/judicial/1978deci/6-72.htm
Chain Letters - Description of chain letters, why people think they can work, why they can't work. Extensive links. - http://www.cs.rutgers.edu/~watrous/chain-letters.html