Its easy to forget about sources you visited once and to which you meant to return. British History Online is one such, a free digital library containing some of the core printed primary and secondary sources for the medieval and modern history of the British Isles.
An initiative of the Institute of Historical Research and the History of Parliament Trust, the site promotes the study of history by publishing often rare resources for their historical value, cross-searchable, in one place and without charge. Registration is asked.
Samuel Lewis's dictionary of Scottish places (1846);
Eneas Mackenzie's 1827 account of the city of Newcastle;
Later records of the barony of Appleby, published by the Cumberland and Westmorland Antiquarian and Archaeological Society;
Volumes 3 and 4 of the Victorian County History for Worcestershire
Volumes 3 and 4 of the Victoria County History for Surrey
Volume 2 of the Victorian County History for Hertfordshire and North London
Volume 3 of the Victorian County History for Berkshire
Victorian County History for metropolitan Essex and East London
Victorian County History for Winchester and the Isle of Wight