Europeana is work in progress, but already has nearly 6,300 hits for ephemera, mainly so far from The European Library and Hispana. Additionally, there are over 35,000 entries under postcard (nearly 27,000 under Postkarte), many part of Europeana's major 1914-1918 project.
The list of Europeana participants includes the University of Ghent, which will contribute Posters of the late 19th century and ephemera.
This will be a major resource. Developments can be followed on Facebook, on a blog and on Twitter.