Democratic: Senator John Kerry (MA) and Senator John Edwards (NC): Kerry-Edwards 2004, Inc., U.S. Senate office, P2000 page   (nominating process)
 

Independent: Ralph Nader (CT) and Peter Miguel Camejo (CA): Nader for President 2004, Citizen Works, Democracy Rising, P2000 page, Nader 2004 Draft Committee
 

Green: David Cobb (CA) and Pat LaMarche (ME): Cobb/LaMarche 2004
former candidates/prospective candidates: Paul Glover (NY), Kent Mesplay (NY), Carol Miller (NM), Lorna Salzman (NY), Peter Camejo (CA), Sheila Bilyeau (VA), Ralph Nader (CT)
 

Libertarian: Michael Badnarik (TX) and Dr. Richard Campagna (IA): Badnarik for President, Dr. Richard V. Campagna   (nominating process)
 

Constitution: Michael Peroutka (MD) and Dr. Chuck Baldwin (FL):Peroutka 2004, Inc., Institute on the Constitution, "Chuck Baldwin Live"   (acceptance remarks)
 

Socialist: Walter Brown (OR) and Mal Herbert (VT): Brown/Herbert in 2004, Socialist Party U.S.A. Campaign Page   photo  (nominating process)
 

Socialist Workers Party: "Róger Calero, 35, is the associate editor of the Spanish-language magazine Perspectiva Mundial and a staff writer for the Militant. He lives in Newark, New Jersey. Calero has lived in the United States since 1985, when his family moved from Nicaragua to Los Angeles.  Arrin Hawkins, 29, is a garment worker in New York.  She was the Socialist Workers Party candidate for lieutenant governor of New York in 2002." >>

Socialist Equality Party: In January 2004 the Socialist Equality Party announced Bill Van Auken for president and Jim Lawrence for vice president.  "Bill Van Auken, 54, is a full-time writer for the World Socialist Web Site. He lives in New York City.  Jim Lawrence, 65, is a retired auto worker, who worked at General Motors plants in the Dayton, Ohio, area for 30 years." 
 

General Resources
Charles O. Jones.  June 2004.  "Bush and Kerry: Questions About Governing Styles."  Washington, DC: The Brookings Institution. [Policy Brief #134]

Political Activity-Hatch Act (U.S. Office of Special Counsel)
-Sept. 8, 2004 Press Release - Sending politically partisan electronic mail messages while on duty.
 

More
The field of Democratic candidates (and non-candidates).

The Natural Law Party which ran Dr. John Hagelin in 1996 and 2000, closed its national headquarters in April 2004.  Hagelin backed Democratic candidate Dennis Kucinich (D-OH) in the primaries. 
Natural Law Party, Institute of Science, Technology and Public Policy

Some Greens advanced former Georgia Congresswoman Cynthia McKinney (D) as a possible presidential candidate, but she ruled it out.

Many more individuals who you've probably never heard of at presented themselves as candidates or were advanced as possible candidates.