There are many websites offering screenplays, books, poetry and more. Not all of them are copyright compliant however so be careful how you use materials and check they are from reliable sources.
Here is a selection you may be interested in:
Project Gutenberg. Includes literature that is typically out of copyright. It includes many historically important documents (especially American ones) and authors such as Shakespeare, Milton and Dickens. It is full text and free to access.
The First World War Poetry Digital Archive. Contains over 7,000 items of text, images, audio and video, including collections of highly valued primary material from major poets of the period, such as Wilfred Owen, Isaac Rosenberg, Robert Graves, Vera Brittain, and Edward Thomas.
Discovering literature: Romantics and Victorians. British Library website with full text books and poems, themes and author information
British Council Writers Directory. 715 UK writers
Romantic Circles. A refereed scholarly website devoted to the study of Romantic-period literature and culture
Folger Digital Texts. Shakespeare's plays online
The Blake Archive. The works of William Blake
The Victorian Web. All aspects of Victorian society
The online books page. A website that facilitates access to books that are freely readable over the Internet
Luminarium. Anthology of English literature from the medieval to the restoration period
Outside the book. Open University produced series of quirky videos on comedy, tragedy, two styles of love, the author
OU on Sky Arts - My Shakespeare. Series of documentaries by leading actors telling the stories and behind some of Shakespeare's greatest plays
Shelley-Godwin Archive. Digitised manuscripts of Percy Bysshe Shelley, Mary Wollstonecraft Shelley, William Godwin, and Mary Wollstonecraft
Wired for Books. Poems, stories, plays, essays, lectures, and interviews with authors
Baldwin Library of Historical Children's Literature. Possible to search for just digitised texts
Chawton House Library. Some useful biographies of women writers
Bibliomania. Classic Fiction, Drama, Poetry, Short Stories and Contemporary Articles and Interviews
GlobePlayer. Shakespeare's Globe Theatre - some free content, mostly interviews with actors and directors