National Constitution Center. The center, created by P.L. 100-433, the Constitution Heritage Act of 1988, is independent, nonpartisan, and nonprofit. It is located on the Independence Mall in Philadelphia. Visitors to the National Constitution Center, which opened on July 4, 2003, receive copies of a pocket-sized edition of the Constitution with their admission

http://www.constitutioncenter.org
Constitution (full-text):
http://www.constitutioncenter.org/explore/TheU.S.Constitution/index.shtml
U.S. Pocket Constitution (PDF download)