http://wellcomelibrary.org (for access to Wellcome catalogue and Wellcome images. The Wellcome Library also has many e-books, digitised sources and a moving image collection (e.g. films on shell-shock). For those who can visit in person, it holds many archival resources and is a wonderful place to work. There is a huge digitisation project, the Digitised Mental Health Care archive, which has made the records of e.g. Ticehurst, Manor House Asylum, and the York Retreat available, as well as the archives of prominent psychiatrists, the Mental After Care Association, and MIND.
Via Warwick University Library
Newspapers - include The Times and many other large circulation newspapers though the years covered vary greatly. Nineteenth-Century British Newspapers, a collection of provincial newspapers which include reports on local asylums, court cases involving insanity plea, etc.
Databases include British Periodicals online (a huge range of periodical literature, general interest journals with numerous articles on mental health, asylums, etc) from the late seventeenth-century to the twentieth; ECCO (Eighteenth-Century Collections On-line); Dictionary of National Biography (for information on 'famous' figures e.g. John Conolly, Henry Maudsley); House of Commons Parliamentary Papers - a useful guide to this source is to be found on the Centre for the History of Medicine website (Warwick) http://www2.warwick.ac.uk/fac/arts/history/chm/events/ass/hcpp-handout.pdf (material on asylums, inquiries, legislation, Lunacy Commissioners and Board) and Old Bailey on-line.
Check out History Databases for more leads (via Library)
Modern Records Centre at Warwick. The archive contains rich holdings on the National Asylum Workers Union, Social Work archive, and much more. Search under Guide to to Resources on Mental Health.
Open Access (i.e. no need to go via University Library)
Eugenics Review is available electronically (this is hard to search, but a good place to look up specific articles)
Victorian Web direct access to a rich range of medical and literary resources on health matters (essays and extracts) http://www.victorianweb.org/
The National Archives Discovery catalogue gives a massive amount of data on archival collections throughout England and Wales, access to resources and other databases http://www.nationalarchives.gov.uk/
Internet resources are plentiful, some are general, other sites focus on specific issues! Use them with discrimination. Useful sites are e.g.
Case Histories from the History of Psychiatry
Mental Health Time Line, Middlesex University
Literature, Arts and Medicine, New York University Database (search film, literature, etc with key words)
There are also numerous relevant films: The Madness of King George; One Flew over the Cuckoo's Nest; The Snake Pit; Gaslight; Regeneration; Let there be Light; shell shock archival film