Diccionarios
Ayto, J. 1993. Dictionary of Words Origins: Histories of More than 8,000 English-Language words. Arcade Publishing.
Bradley, H. (ed.) 1986 [1891]. A Middle English Dictionary, containing words used by English Writers from the Twelfth to the Fifteenth century, by F.H. Stratmann. Oxford: University Press.
Crystal, D. 20015 [1981]. A Dictionary of Linguistics and Phonetics. London: Blackwell.
Jones, D. et al. 2011. Cambridge English Pronouncing Dictionary. Cambridge: Cambridge U. P.
Onions, C. T. (ed.), W. S. FRIEDERICH & W. BURCHFIELD. 1985 [1966]. The Oxford Dictionary of English Etymology. Oxford: University Press.
Skeat, W. W. 1983 [1882]. An Etymological Dictionary of the English Language. Oxford: Clarendon Press.
Trask, R. L. 1993. A Dictionary of Grammatical Terms in Linguistics. London: Routledge.
Upton, C. et al. 2001. The Oxford Dictionary of Pronunciation for Current English. Oxford: University Press.
Wells, J. C. 2008 [1990]. Longman Pronunciation Dictionary. London: Longman.
General
Barber, Ch. 1993. The English Language: A Historical Introduction. Cambridge: University Press.
Bragg, M. 2003. The Adventure of English. The Biography of a Language. London: Hodder & Stoughton.
Brook, G. L. 1968. A History of the English Language. London: André Deutsch.
Burchfield, R. W. 1985. The English Language. Oxford: University Press.
Claiborne, R. 1991. The Life and Times of the English Language. London: Bloomsbury.
Campbell, L. 1998. Historical Linguistics. Edinburgh: University Press.
Fernández, F. 1982. Historia de la Lengua Inglesa. Madrid: Gredos.
Freeborn, D. 1992. From Old English to Standard English. London: MacMillan.
Fisher, O. et al. 2000. The Syntax of Early English. Cambridge: University Press.
Lightfoot, D. 2006. How New Languages Emerge. Cambridge: University Press.
Middle English
Blake, N. F. (ed.). 1992. The Cambridge History of the English Language. II 1066-1476. Cambridge: University Press.
Burrow, J.A. & T. Turville-Petre. 2008 [1992]. A Book of Middle English. Oxford: Blackwell Publishing.
Fisiak, K. 1968. A Short Grammar of Middle English. Oxford: University Press.
Horobin, S. & J. Smith. 2002. An Introduction to Middle English. Edinburgh: University Press
Sisam, K. & J. R. R. Tolkien. 2005. A Middle English Reader and Vocabulary. New York: Dover Publications.
Smith, J. J. (ed.). 1988. The English of Chaucer and his Contemporaries. Aberdeen: University Press
Mossè, F. 199110 [1952] A Handbook of Middle English. London: The Johns Hopkins University Press.
Wardale, E. E. 1972. An Introduction to Middle English. London: Routledge & Kegan Paul.
Wright, J. & E. Wright. 1967. An Elementary Middle English Grammar. Oxford: University Press.
Modern English
Barber, Ch. 19972 [1976]. Early Modern English. Edinburgh: University Press.
Brook, G. L. 1976. The Language of Shakespeare. London: André Deutsch.
Dobson, E. J. 1985. English Pronunciation 1500-1700. 2 vols. Oxford: University Press.
Ekwall, E. 1975. A History of Modern English Sounds and Morphology. Oxford: Basil Blackwell.
Görlach, M. 1991. Introduction to Early Modern English. Cambridge: University Press.
Nevalainen, T. 2006. Introduction to Early Modern English. Oxford: University Press.
Wright, J. 1924. An Elementary Historical New English Grammar. Oxford: University Press.
Oxford English Dictionary Online (OED)
http://www.oed.com/
Middle English Dictionary
http://quod.lib.umich.edu/m/med/
History
http://www.thehistoryofenglish.com/index.html (How English went from an obscure Germanic dialect to a global language)
http://www.bl.uk/learning/langlit/evolvingenglish/accessvers/index.html (BBC -Learning English Timeline)
Middle English Texts
http://www.lib.rochester.edu/camelot/teams/tmsmenu.htm (Middle English Texts)
http://www.luminarium.org/medlit/ (Anthology of Middle English Literature)
Chaucer
http://metro.fas.harvard.edu (Middle English Teaching Resources Online_Chaucer)
The Glossarial Index of Middle English (mostly Chaucer): http://www.hti.umich.edu/english/gloss/
A collection of links to online resources about Chaucer for both students and teachers, vetted by scholar: http://chaucermetapage.org/?q=chaucer%2Fzatta%2F14thcent.html
Images
D-Scriptorium, an amazing site for digital images of medieval manuscripts: http://www.byu.edu/~hurlbut/dscriptorium/
The Bodleian Library's online medieval manuscript images: http://www.bodley.ox.ac.uk/dept/scwmss/wmss/medieval/browse.htm