This website has slip opinions, electronic versions of the United States Reports (volume 502 onward), and other useful information for Supreme Court cases. Authors of that site caution users that print versions are the official source. http://www.supremecourtus.gov
This website provides online access to Supreme Court decisions since May 1990 through Project Hermes. Site also has over 300 of the most important historical cases available online in a separate file. http://supct.law.cornell.edu/supct
This website has case decisions from 1937-1975. Users can search by case name or keyword.
http://supcourt.ntis.gov/
FLITE = Federal Legal Information Through Electronics
This website has access to decisions from 1893 to the present. Users can search by year, case name, full text, or citation. http://www.findlaw.com/casecode/supreme.html