Grace`s Guide at https://www.gracesguide.co.uk/Main_Page or more correctly, Grace's Guide to British Industrial History, is a really useful one as it gives biographies of companies, so if you collect trade cards and ephemera you will find a lot of information here. They have also digitised many early magazines and guides, starting from 1833, and you can download those as PDFs, though they do charge for this.
And as this is a continually updating site, they are always looking for volunteers to send in any information to add to their records.
New York Public Library at https://digitalcollections.nypl.org/collections/cigarette-cards is a vast collection of cigarette cards and ephemeral items, pretty much all digitised front and back, and it was the collection of just one man, George Arents Jr., who collected everything to do with the story of tobacco and cigarettes, and bequeathed it to the library when he died in 1960.
George Arents Jr. was born in 1875, and tobacco was in his blood, for his uncle was none other than Major Lewis Ginter, who became a partner in the firm of Allen and Ginter in the year that George was born. And Allen and Ginter were one of the first tobacco firms to distribute cigarette cards inside their packets. In 1890 they became part of the American Tobacco Company, and George Arents Jr. would even work there.
Dinosaur Cards - https://www.dinofan.com/Collectibles/ByCategory/ByCategoryMenu.aspx
Flag Cards - https://www.flagmakers.co.uk/info/flag-memorabilia-collectables/cigarette-trade-cards-portraying-national-flags-emblems/
Football Cards - http://cartophilic-info-exch.blogspot.co.uk/