Supreme Court — High court opinions from 2002 onward, oral arguments, and more. The Law Library of Congress has digitized the Supreme Court's United States Reports from 1754 to 2003, so the complete run is free and available online.
Constitution of the United States of America: Analysis and Interpretation — Analysis and interpretation of the U.S. Consitution and all amendments. This volume is richly annotated with references to cases decided by the Supreme Court. This page, at Govinfo, includes previous editions and supplements back to 1992.
Court Locator — This page has a clickable US map to help find US courts and court officials. Detailed information includes phone number, street address and Google map data to court locations.
Fedworld: Supreme Court Decisions — search for Supreme Court cases decided between 1937 and 1975. Cases are in plain text format.
FindLaw: Cases and Codes: Supreme Court Opinions — offers a searchable database of cases decided from 1893 to the present. Files are in html format.
Foreign Intelligence Surveillance Court — collection of publicly available filings of the U.S. Foreign Intelligence Surveillance Court. This is the judicial body which oversees activities authorized under the Foreign Intelligence Surveillance Act.
LII: Supreme Court Collection — Supreme Court Decisions from 1990 to the present. Documents are in html or WordPerfect format. Recent documents are in html and pdf format.
SCOTUS blog — Supreme Court of the United States (SCOTUS) blog, covers cases before the court. Also hosted here is the SCOTUS Wiki which gathers briefs, articles and opinions on cases and 'petitions to watch.' Includes commentary and analysis, and links to press coverage. This looks like an excellent source for current, reliable information about the Supreme Court.
Supreme Court Nomination Hearings — PDF files of the Senate Judiciary Committee confirmation hearings for successful Supreme Court nominees (that is, those who became justices). Available hearings cover the period from the nomination of John Paul Stevens (1975) to the present.
U.S. Courts — homepage for the Judiciary, this site provides information on the structure and operation of the US court system, along with full-text publications such as the journal Federal Probation and the guide Understanding the Federal Courts available as a PDF.