Museum of London

The Museum of London has wonderful collections of ephemera and is actively surfacing them, notably the tinsel prints, valentines, Christmas cards and trade cards.
The Collections pages enable you to read about the collections and to search (here I searched for suffrage).

(c) Museum of London

(c) Museum of London

As well as the museum's website Ellie, the Project Assistant focussing on ephemera, is blogging regularly about progress.

The Museum's commercial site has thousands of images which can be searched and ordered.