Dr. John Jaeger, a librarian at Dallas Baptist University has compiled a list of web sites that offer access to lists of Dissertations/Theses.
Abes: Agence Bibliographique de l'Enseignement Superieur http://www.abes.fr/abes/DesktopDefault.aspx?Loupe=Moin Citations to French dissertations.
Australian Digital Theses Program http://adt.caul.edu.au This site provides both citation and full-text access to a few thousand theses and dissertations published in Australia.
The British Library http://www.bl.uk/services/bsds/dsc/theses.html The British Library provides access to citations of theses from British universities (most doctoral theses from the early 1970s onward), from the United States (475,000 doctoral theses), and from Canada (several hundred doctoral theses from 1980 forward).
Center for Research Libraries http://www.crl.edu Twenty thousand doctoral dissertations from outside of the United States and Canada are searchable from this site. Items can be ordered through ILL by students, faculty, and staff.
Cybertheses http://www.cybertheses.org/cybertheses/cybertheses.html Cybertheses allows access to citations of French dissertations from 1972 to the present.
Digital Library and Archives http://scholar.lib.vt.edu/theses Digital Library and Archives allows searching for citations and abstracts of over 6,700 theses and dissertations. Free full-text access is provided for over 4,500 of these items.
Directory of Dissertations in Progress http://www.historians.org/pubs/dissertations/index.cfm "The Directory contains 3,804 dissertations in progress at 170 academic departments in Canada and the U.S." This is a citation database of dissertations in progress in the area of history.
Dissertation.com http://www.dissertation.com Dissertation.com has just a few hundred dissertations and theses in its collection, but the site allows free, full-text access to the first twenty-five pages of each item.
Doctoral Dissertations in Musicology http://www.music.indiana.edu/ddm This is an international database of citations for dissertations in musicology that contains over 12,000 records. Dissertations are from approximately 1950 to the present.
NDLTD - Networked Digital Library of Theses and Dissertations http://www.ndltd.org NDLTD provides access to citations from thousands of digital dissertations and theses that are in PDF format. A significant number of these resources are freely available in full-text and can be viewed online.
PhdData: The Universal Index of Dissertations in Progress http://www.phddata.org PhdData has citations from several thousand dissertations in progress from various parts of the world.
Proquest Digital Dissertations http://wwwlib.umi.com/dissertations Proquest provides the past two years of citations and abstracts in their Digital Dissertations database at no cost.
Theses Canada Portal http://www.collectionscanada.ca/thesescanada/index-e.html
Theses Canada provides access to bibliographic citations for all the theses in the National Library of Canada Theses Collection. Access to full-text theses is available for all items published between January 1, 1998 to August 31, 2002.
Theses Link Collection http://www.mkengel.de/thesis/thesis.htm This site gives links to dissertation/theses search sites in many different countries, including Austria, Germany, The Netherlands, Sweden, and Norway.
TREN: Theological Research Exchange Network http://www.tren.com TREN provides citations to 6,800 theological theses/dissertations and conference papers. Items can then be purchased through this site. The opening page actually states that they have 10,000 theses/dissertations, but the search page allows searching of 6,800 items.