Many excellent websites from the years 2005-2015 have sadly disappeared, such as www.cretaceousfossils.com. Other authors have moved to a blog or a simpler Facebook account, like Frédéric Diebold.
Albian fossils of the Anglo-Paris Basin. David Jolly's website in French on fossils from the Albian belt of the Anglo-Paris Basin : Seine-Maritime, Folkestone, Wissant, Ardennes, Meuse et Aube.
The Albian ammonites of Wissant. This educational website in French, by natural science teachers Francis Amédro and Richard Platevoet, describes the Albian stratigraphy of Wissant (Pas-de-Calais, facing Dover) and provides information on paleogeography, sedimentology, and ammonite evolution. Francis Amédro is also a leading expert on Albian and Turonian ammonites.
Fossils of the Gault clay. An award-winning English-language website by the late Jim Craig, maintained by Fred Clouter. It features beautiful photographs of ammonites from Folkestone.
Ammonites and other fossils. Cyril Beaudouin's large website features diverse fossils from the Triassic to the Tertiary period, for example, 13 pages of profile pictures of ammonites just for the Albian!
Atlas of Aptian pyritic ammonites from the Alps of Provence. Site created by Gérard Thomel and his daughter Marie-Claire Picollier-Thomel.
Ammonites from Vendée. Excellent recent website by Patrick Bohain on the ammonites of the Jurassic period in the Vendée region (atlantic coast of France).
GB3D Type Fossils. A database of specimen types (mostly ammonites) held in British museums, with downloadable high-resolution images. It appears to have been inactive since 2014, following museum budget cuts by David Cameron's government.
Chalk cliffs. Site in French on the cliffs of the Seine-Maritime coastline, with videos and numerous photos of Cenomanian ammonites (menu Faune/Macrofaune/Céphalopodes).
The Fossil Forum. An international site where members post great photos of their specimens. Already nearly 500 ammonites!
Echinologia is a very comprehensive website about sea urchins, created in 2001 and still active. I use this site to identify the sea urchins that I also have in my collection.