The following sites are recommended:

Imaginative Book Illustration Society (IBIS):

(For book search) International League of Antiquarian Booksellers:

Antiquarian Booksellers Association:

Provincial Booksellers Fairs Association (PBFA):

The Ephemera Society:

Quad Royal: A very interesting blog about all aspects of posters.

And for any country blues enthusiasts: a 24 hours country blues internet radio station (Juke radio):