A lot of digital resource websites for history are, quite honestly, badly designed. It's usually down to high demand, under resourcing, or a delightful mix of both. As for recommendations - well, it depends entirely on what you want to find in the archives!

JSTOR is probably your best starting point. Although JSTOR is famously mostly as the leading archive of academic journals and only really accessible in full if you're attached to a university or able to go to a university library, JSTOR also has a substantial catalogue of primary sources available to the public. For example, if I search without logging in for documents containing the term "labor" between 1650 and 1850, I get 1,840 results that I can read and download PDF files of as a member of the public. These are often old 19th century journals or circulars, but there are other things in there as well. If you went to a university, you should also check if their alumni department offers an alumni subscription to JSTOR. It's increasingly common for universities to give their alumni lifetime access to their JSTOR catalogue, or most of it, for free.

For American history, the Library of Congress is an incredible and under-rated resource with literally tens of thousands of digitised items for you to look through, including an extensive newspaper digitisation series called Chronicling America. The UK's National Archives have less digital content available but still an impressive selection. The two stand-out curated digital collections would be Anthony Edens' private papers and the log/journal collection of exploration ships. There are other scattered, partly-digital collections as well, for example the select collection of declassified UK Cabinet papers intended to help students in the UK with their 20th century history courses. These make for fascinating insight into the decision-making of Britain's political leadership behind closed doors. You can also check out British History Online which has several hundred digitised primary sources available for free, provided the Institute of Historical Research and the History of Parliament Trust.

Archive.org is another great resource that is massively under-utilised. You might know it better as the home of the WaybackMachine, the tool that lets you visit old versions of a website. But it is also home to close to 50million other digitised records, including a lot of history resources uploaded by libraries and archives around the globe. For example, here is a fully digitised copy of a speech given by Henry Bleby - a prominent anti-slavery activist - to the Massachusetts Anti-Slavery Society in 1858. There are tens of thousands of records like this scattered around Archive.org. Don't underestimate Google Books, either, which has a large if completely random collection of digitised books that are no longer in copyright, including publications from centuries ago.

NewspaperArchive.com is sadly a paid service, but one with an impressive back catalogue of material from around the world, including newspapers it's very hard to get hold of anywhere else. They bill themselves as a family history resource but in reality their search tools can be used for any kind of historical research, and I've been able to use their Caribbean archives with great success before. Always look and see if there's a free alternative for a newspaper collection you want, though, or if a local library has an existing subscription to a digital archive.

One of my personal favourite online archives, though it's only small, is the Digital Library of the Caribbean. It holds more than 2.5million pages of historical and modern material from the Caribbean region. Some of it is utterly random, but there's hidden treasure in there. For example if you go into the Barbados Catalogue, item 10 is a collection of 2,334 issues of a 19th century Barbadian newspaper. Item 11 is a single newspaper clipping about a musical festival. But it is an incredibly valuable resource for anyone who has an interest in this part of the world.

There are other free digital resources out there - it all depends on what your interests are specifically and what you're doing your research for.