Many Government reports can be found in LionSearch. Use the Government documents facet on the left after running your search.
Executive Branch Documents can often be found in LionSearch or The CAT. Search by topic and/or agency (Civil Rights Commission or Dept. of Justice for example).
Most recent reports can be found on the Web at www.usa.gov.
Some Presidential messages (speeches, news conferences, etc.) are online through the American Presidency Project.
Historic Supreme Court decisions and the texts of laws can be found in HeinOnline.