LII Supreme Court Decision: Presidency - Case law dealing with the issues of the presidency. - http://www2.law.cornell.edu/cgi-bin/foliocgi.exe/historic/query=[group+f_presidency:]/doc/{@1}/hit_headings/words=4/hits_only?
Center for Study of the Presidency - Devoted to the study of the American Presidency, historical and current information on the president and the presidency along with political and government links - http://www.cspresidency.org/