Wikipedia A good article on forgers and forgeries. There is also a list of worthwhile links at the bottom of the piece, sime of which are repeated below.
Tedesco Described as a "massive bibliography of stamp fakes and forgeries". The author (Morten Munck) states, "I created to solve the problem of stamp forgeries – once and for all. My vision is to display all forgeries ever created next to a genuine stamp for easy comparison". At the time of writing (May 2017) it covers 217 countries and, of course, deals with all issues, not just first issues.
It also contains the full text of the 3rd edition (1903) of R. B. Eareé's Album Weeds, and the Spud Papers, describing the Spiro forgeries.
World Forgery Catalogue Links to a pdf copy of G. Kock's 1998 book.