General
MLA International Bibliography ['provides a classified listing and subject index for books and articles published on modern languages, literatures, folklore, and linguistics']
ProQuest Dissertation Express [database of MA and PhD theses published in North American and Europe since 1861]
Networked Digital Library of Theses and Dissertations (NDLTD) ['an international organization dedicated to promoting the adoption, creation, use, dissemination and preservation of electronic analogues to traditional paper-based theses and dissertations']
DART-Europe E-theses Portal (DEEP) ['DART-Europe is a partnership of research libraries and library consortia who are working together to improve global access to European research theses']
EThOS-Beta: Electronic Theses Online Service [database of MA and PhD theses published in UK]
JSTOR [database of journal articles]
Zetoc ['provides access to the British Library's Electronic Table of Contents of around 20,000 current journals and around 16,000 conference proceedings published per year']
Dialnet [database of academic articles published in Spain and in international journals]
WikiBibliography of English Language Studies [a working bibliography of English linguistics and medieval English language and literature; maintained by Professor Yoko Iyeiri (Kyoto University)]
Historical Sociolinguistics and Sociohistorical Linguistics: Cumulative Bibliography
Language Change Database [a fully searchable resource with 'the results of a large number of articles that document how the English language has changed in the course of its history']
Old English
OEN Bibliography Database ['Currently contains the annual bibliographies from 1973-2006—over 21,000 entries, with new items added annually'; registration is required]
Beowulf Bibliography, 1990-2012 [by Kevin Kiernan (University of Kentucky)]
Middle English
Thirty-Year Working Bibliography for Chaucer and Middle English Literature 1970-2000 [by Derek Pearsall]
Chaucer Bibliography Online [includes Chaucer studies from 1975 until the present]
Essential Chaucer ['a selective, annotated bibliography of Chaucer studies from 1900-1984']
The Chaucer Review: An Indexed Bibliography Vols. 1-30
CHAUCER: A Semi-systematic, Serendipitous Bibliography [compiled by Alan Baragona (Virginia Military Institute)]
Modern English
English as a world language in the long 18th century ['A preliminary bibliography compiled by Anne Coyle, 1999']
Libraries
Libweb: Library Servers via WWW
WorldCat [extensive links to libraries in the world]
National Libraries of the World: Address List (Wikipedia)
Library Hub Discover [catalogues of major university and national libraries in UK]