An excellent find! Contains over 3000 members who discuss different aspects of history. You're going to get a few loonies in a group of people that size but it seems well-organised and efficiently run. Looks like there's a few battles of ideas going on there too, which is cool.
This is the anthropological artfefacts databast at the Smithsonian Museum. Seems to especially cover the Americas and Egypt, although probably has stuff from all over the place and you'd expect it to be well-organised. Over 2 million artefacts.
An excellent collection of sites by those awesome librarians at the University of Washington about British and Irish history. Well-organised and good quality.
This is the modern history sourcebook. Just as good as the medieval and ancient, it's a must for anyone researching the modern period. Excellent collection and wonderfully organised.
This site has a collection of "60,000 documents detailing the political and social history of the United States". Seems well organised; run by the Gilder Lehrman Institute of American History.
"A listing of over 5000 websites describing holdings of manuscripts, archives, rare books, historical photographs, and other primary sources for the research scholar. All links have been tested for correctness and appropriateness."
Has some relevant curriculum materials for Australian history, however I can't help but feel that this kind of thing is like a shining brand-new horse-drawn carriage at the beginning of the twentieth century, unknowing that it has already been superseded...
This is a thorough and well-organised collection of sources related to legal history. Quite useful for any political, legal or even just general historical research.
Enormous collection of older books now out of copyright on a wide array of topics. Some specialist topics here suitable for senior secondary/tertiary research and organise well under topics.
An enormous collection of links covering a wide array of regions and all time periods. It has primary texts, maps, diagrams, statistics, all types of historical sources. Well-organised and searchable.