"British History Online is a collection of nearly 1300 volumes of primary and secondary content relating to British and Irish history, and histories of empire and the British world. BHO also provides access to 40,000 images and 10,000 tiles of historic maps of the British Isles." (Website)
Includes more than 1100 volumes of open access content. BHO is curated by the Institute of Historical Research, University of London.
Explore their online collections and virtual galleries, search their millions of artifacts, and even visit the museum virtually ("Did you know that the Museum is the world's largest indoor space on Google Street View?").