A great source of old maps
English Heritage have a dynamic site. Rather than giving separate links, start from the home page to find
Knowing which archive to visit is a big issue especially for amateurs. This new site called access to archives could be the answer to your prayers.
The Public Records Office is a 'must visit' location for every researcher. They are both welcoming and helpful for all researchers. You can check out their catalogues including PROCAT where you can see what documents are available.
North Yorkshire has an excellent on-line archive search. Another excellent, local resource is the Borthwick Institute.
Genealogy support some excellent resources such as a collection of maps.