Credo Reference and the Gale Virtual Reference Library are both excellent electronic reference tools.
Library of Congress, Prints and Photographs Division, LC-USZC4-3072. See www.slaveryimages.org, compiled by Jerome Handler and Michael Tuite, and sponsored by the Virginia Foundation for the Humanities and the University of Virginia Library. Image reference: Berryman128.
Africa and the Americas [electronic resource] : culture, politics, and history : a multidisciplinary encyclopedia / edited by Richard M. Juang and Noelle Morrissette ; Melissa Fullmer, editorial assistant. Santa Barbara, Calif. : ABC-CLIO, c2008 (Boston, Mass. : Credo Reference, 2012).
Dictionary of Afro-American slavery / edited by Randall M. Miller and John David Smith. Westport, Conn. : Praeger, 1997.
Encyclopedia of African American history, 1619-1895 [electronic resource] : from the colonial period to the age of Frederick Douglass / editor in chief, Paul Finkelman. New York : Oxford University Press, 2006.
Encyclopedia of the middle passage / edited by Toyin Falola and Amanda Warnock. Westport, Conn. : Greenwood Press, 2007.
Klein, Martin A. Historical dictionary of slavery and abolition. Lanham, Md. : Scarecrow Press, c2002.
Slavery and slaving in world history : a bibliography / Joseph C. Miller, editor.
Societies after slavery : a select annotated bibliography of printed sources on Cuba, Brazil, British colonial Africa, South Africa, and the British West Indies / Rebecca J. Scott ... [et al.], editors. Pittsburgh, Pa. : University of Pittsburgh Press, c2002.
The trans-Atlantic slave trade [electronic resource] : a database on CD-ROM. Cambridge, UK : Cambridge University Press, 1999.
Africa, Asia, and South America since 1800 : a bibliographical guide / compiled by A.J.H. Latham. Manchester ; New York : Manchester University Press ; New York : Distributed exclusively in the USA and Canada by St. Martin's Press, c1995.
Bibliography of Slavery and World Slaving. Online bibliography.
John David Smith. Black slavery in the Americas : an interdisciplinary bibliography, 1865-1980 / compiled by John David Smith ; foreward by Stanley L. Engerman. Westport, Conn. : Greenwood Press, 1982.
Joseph C. Miller. Slavery : a worldwide bibliography, 1900-1982 / Joseph C. Miller. White Plains, N.Y. : Kraus International, 1985.
Oxford bibliographies. African studies [electronic resource]. / editor-in-chief, Thomas Spear. [New York] : Oxford University Press.
Oxford bibliographies. Latin American studies [electronic resource] / editor in chief: Ben Vinson. Oxford : Oxford University Press.
Peter C. Hogg. The African slave trade and its suppression; a classified and annotated bibliography of books, pamphlets and periodical articles. London, F. Cass .
Robert Edgar Conrad. Brazilian slavery : an annotated research bibliography / Robert Conrad. Boston : G. K. Hall, c1977.
Slavery and slaving in world history : a bibliography / Joseph C. Miller, editor. Armonk, NY : M.E. Sharpe, c1999.
David Eltis. Atlas of the transatlantic slave trade / David Eltis and David Richardson ; foreword by David Brion Davis ; afterword by David W. Blight. New Haven : Yale University Press, c2010.
James Walvin. Atlas of slavery / James Walvin. Harlow, England ; New York : Pearson Longman, 2006.