⇔ 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, digitised front and back, and it was the collection of one man, who collected everything to do with tobacco and cigarettes, and bequeathed it to the library on his death in 1960. George Arents Jr. was born in 1875, and tobacco was in his blood, his uncle being Major Lewis Ginter, who, in the year George was born, became a partner in the firm of Allen and Ginter, one of the first tobacco firms to issue cigarette cards inside their packets. In 1890 they became part of the American Tobacco Company, and George Arents Jr. even worked there.
⇔ Flag Cards - at - https://www.flagmakers.co.uk/info/flag-memorabilia-collectables/cigarette-trade-cards-portraying-national-flags-emblems/
This site deserves a mention for they are a commercial flagmakers that have devoted a page of their website to cards. So if you are looking for a flag, do please ask here first by way of thanks! And don`t forget to mention their flag card page.
⇔ Football Cards at http://cartophilic-info-exch.blogspot.co.uk/
Our readers rate this website very highly, for it aims to include every football card that has ever been issued, from the very earliest tobacco card of the 1880s right up to the most recent images of the 2022 World Cup, and in addition cover items of all sorts, silks, stickers, advertising cards etc.
There are also checklists of many sets and, as a real bonus, details of all the sets of general interest where just one card within it shows a footballer! An amazing site.