I have used a large number of resources in compiling this site. I cannot guarantee that the list will ever be complete, but it will contain a large majority of the sources that I have used, and certainly the most frequently-used sources.
John Emms, Play the Open Games as Black (Gambit, 2000). Karsten Muller and Martin Voigt, Danish Dynamite (Russell Enterprises 2003). Jude Acers and George Laven, The Italian Gambit and a Guiding Repertoire for White- E4! (Trafford Publishing 2006). Christoph Scheerer, 2011, Blackmar-Diemer Gambit (Everyman Chess, 2011). Kaissiber magazine (maintained by Stefan Bücker). Stefan Bücker, 1988, Englund Gambit- Drei Gambits in Einem. Marc Esserman, Mayhem in the Morra (Quality Chess 2013) John Shaw, The King's Gambit (Quality Chess 2013)