Blogs
General
OED blog [Check the categories 'History of English' and 'Varieties of English' in particular!]
Language Log [The link is the archive for 'historical linguistics'.]
Linguistics Research Digest ['aims to provide up-to-date reports on the latest research papers on language issues in an engaging, jargon-free way']
Bas Aarts, GRAMMARIANISM ['A blog about English grammar for teachers']
Bridging the Unbridgeable [a blog for the research project with the same title]
History of the English Language [a blog from Spain]
BBC Culture, 'What the earliest fragments of English reveal'
Marisa Lohr (The Open University), 'From old English to modern English'
Old and Middle English
British Library, Medieval manuscripts blog ['This blog publicises our digitisation projects and other activities.']
Kate Thomas, For the Wynn [a blog about medieval manuscripts by British Library's Digitisation Support Officer]
Leiden Medievalists Blog ['This blog provides a platform for Leiden University medievalists to share their knowledge about the Middle Ages with a broader audience.']
Hana Videen, Old English Wordhord - Old English Word of the Day [originally a temporary exhibition by postgraduate students]
Thijs Porck's blog [Old English, early medieval England and Tolkien]
Eleanor Parker, A Clerk of Oxford ['I blog about the literature and history of medieval England, as well as about saints, churches, folklore, Vikings, poetry, and anything else that interests me.'; See also 'Old English Wisdom'.]
David Beard, Anglo-Saxon Archaeology Blog
Megan Cavell et al., The Riddle Ages (previous blog) [PDE translations of the OE and medieval Latin riddles]
Modern English
Researching Early Modern History: A Blog for Professionals and Students
Early Modern Commons - The Blogroll
Ingrid Tieken-Boon van Ostade, Robert Lowth blog
Ingrid Tieken-Boon van Ostade, Late Modern English letters
Sylvia Morris, The Shakespeare blog
Varieties of English
Separated by a Common Language ['Observations on British and American English by an American linguist in the UK', i.e. Lynne Murphy]