GPO Access provides extensive coverage of Congressional materials. 

An excellent source of Congressional materials: bill information, Public Laws, the Congressional Record, and hearings, committee reports, roll call votes and more.

A hearing is a meeting or session of a Senate, House, joint, or special committee of Congress, usually open to the public, to obtain information and opinions on proposed legislation, conduct an investigation, or evaluate/oversee the activities of a government department or the implementation of a Federal law. Most congressional hearings are published two months to two years after they are held.

Both GPO and Thomas offer topical/keyword searching for Congressional Hearings issued after 1995.

GPO Access http://www.gpo.gov/fdsys/browse/collection.action?collectionCode=CHRG

Thomas http://thomas.loc.gov/home/LegislativeData.php?&n=Reports&c=110

The Congressional Record is the official record of the proceedings and debates of the United States Congress. It is published daily when Congress is in session. The Congressional Record began publication in 1873, and is still published today.

The Congressional Record consists of four sections:

• Daily Digest

• House section

• Senate section

• Extension of Remarks

Debates for sessions prior to 1873 are recorded in The Debates and Proceedings in the Congress of the United States (1789-1824), the Register of Debates in Congress (1824-1837), and the Congressional Globe (1833-1873). These can be accessed through A Century of Lawmaking For a New Nation: U.S. Congressional Documents and Debates.

The Congressional Research Service, an arm of the Library of Congress, serves the legislative process by providing Congress with non-partisan and in-depth legislative research and analysis on a variety of topics. CRS produces or updates more than 3,000 studies and other publications each year, none of which are distributed to the public. However many sites host reports relating to their main mission/interest providing a great public service.

LLRX http://www.llrx.com/features/crsreports.htm
Great overview site explaining what CRS reports are and with many links to various sites hosting them.

Federation of American Scientists http://www.fas.org/sgp/crs/index.html Founded in 1945 by scientists who built the first atomic bombs, FAS works to ensure that public policy is informed by intelligent, accurate scientific research. 

University of North Texas http://digital.library.unt.edu/govdocs/crs/ This academic site is sponsored by ALA and hosts a growing collection of the reports

State Department http://fpc.state.gov/c18185.htm

Reports on Environmental Law and Policy
http://www.ncseonline.org/programs/science-policy/crs-reports hosted by the National Council for Science and the Environment

Reports on Homeland Security/Terrorism and Health Law and Policy  http://www.law.umaryland.edu/marshall/crsreports/index.asp hosted bt the Thurgood Marshall Law Library

Reports on Intellectual Property, Cyberlaw and Electronic Commerce  http://www.ipmall.info/hosted_resources/crs_reports.asp hosted by the University of New Hampshire

Reports on Congress and its Procedures http://www.llsdc.org/crs-report-links hosted by Law Librarians' Society of Washington, D.C.

U.S. Code

Codified (organized by topic) version of all federal laws currently in force. Various sites offer the U.S. Code online, each with slightly different search features and tools. Classification guides show where newly passed legislation will be entered into code. Popular names tables translate the popular name of law to the official title.

Browse the U.S. Code
 http://www.gpo.gov/fdsys/browse/collectionUScode.action?collectionCode=USCODE
Browse the U.S. Code by year since 1994. The Government Printing Office (GPO) offers pdf and text formats.

Browse and Search the U.S. Code and Related Tables
 http://uscode.house.gov/
The House of Representatives Office of Law Revision Council offers additional tools such as a classification guide and popular names table.

U.S. Code and Popular Names Table
 http://www.law.cornell.edu/uscode/text
The Legal Information Institute (Cornell University Law School) also offers a useful popular names table in addition to a searchable version of the U.S. Code.

The U.S. Congressional Serial Set, 1817-1980 contains House and Senate documents and reports on U.S. political, social, cultural, military and ethnic history, as well as international relations, explorations, genealogy, commerce, and industrial development. Its contents come not only from the U.S. Congress, but also include key Executive Department publications. The database contains all publications from the 15th through the 103rd Congresses (1817-1994). Users can search, as well as browse by subject, geographic names, personal names, and an A-Z index. This resource can be used for legislative and historical research.

Additional Resources from GPO  http://www.gpo.gov/help/u.s._congressional_serial_set.htm
Includes numerical lists of documents and reports from 1957 forward as well as schedules of Serial Set volumes from 1987 forward.

The U.S. Statutes at Large is a chronological arrangement of all laws enacted by Congress. The U.S. Code is an updated, subject arrangement of all general and permanent U.S. law so enacted.