General 
Monarchs of Britain
Internet Modern History Sourcebook

Medieval 
Internet Medieval Sourcebook

Renaissance 
Open Source Shakespeare
The Map of Early Modern London
Tyburn Tree: Public Execution in Early Modern England
The Literature Network: Milton

18th-Century 
18th Century History 
The Proceedings of the Old Bailey, 1674-1834
Britain's Prime Ministers
The Diary of Samuel Pepys

Fun stuff
Circolwyrde Wordhord
Geoffrey Chaucer hath a blog
The Skinhead Hamlet
Plushie Shakespeare
Plushie Queen Elizabeth
Plushie Black Death