U.S. District Court (Federal) cases can be found through several websites.
Justia - is a company that offers free links and information on court dockets and filings. This site allows you to track a docket. The information will have the most recent date of an update. More recent docket listing can be found on PACER.
PACER - is maintained by the U.S. government and provides electronic access to federal court cases. While court opinions can be found for free on PACER, other court records in the docket are not free and cost per page to access. An account must created to read court opinions via this site. Please note, it takes 7-10 business days to receive a letter with an authentication token in the mail in order to login to PACER.
Search the most recent opinions of the Court on this site. The opinions of the Supreme Court of the United States are published officially in a set of case books called the United States Reports. This site has access to opinions from 1991-current.
To find additional U.S. Supreme Court decisions, try FindLaw's database of cases from 1760 to present. Supreme Court opinions are browsable by year and U.S. Reports volume number, and are searchable by party name, case title, citation, full text and docket number.