In Brief:
Above I compiled a few links to the webpages that may be useful to metaldetectorists especially interested in identification of coins and some common relics, and preservation of iron artifacts. I also included a list of helpful websites for map researchers, and webpages containing topografic and historic maps (mostly of the New England region, USA).
If you do not see the name(s) of your favorite webpage(s) covering the above-mentioned subjects in my list below, but you believe the website(s) should rightfully be listed here, please do not hesitate to submit a link: