For historical fiction readers and authors, an article at Medieval Histories might be of interest. A non-scientific survey has apparently shown that readers want to read more books set in the Middle Ages but historical fiction authors prefer to write novels set in the 1800s and 1900s.
I know that the Victorian and Regency eras are both big – with readers and writers – in romance and mystery publishing although I have definitely seen a decent number of mysteries set during the Middle Ages as well.
What are your preferred eras for historical fiction? Do you find enough novels set in your favorite period?