some of my standard film reference books i use again and again include:
I COLORI DEL BUIO - IL CINEMA THRILLING ITALIANO DAL 1930 AL 1979 (Luca Rea)
LA COMMEDIA EROTICA ITALIANA - VENT'ANNI DI CINEMA SEXY "MADE IN ITALY" (Michele Giordano)
DELIRIUM - A GUIDE TO ITALIAN EXPLOITATION CINEMA 1975-1979
99 DONNE - STELLE A STELLINE DEL CINEMA ITALIANO (Manlio Gomarasca and Davide Pulici)
JESS FRANCO CHRONICLES (Andreas Bethmann)
FORGOTTEN HORRORS (George F. Turner and Michael H. Price)
THE MEXICAN MASKED WRESTLER AND MONSTER FILMOGRAPHY (Robert Michael Cotter)
...and various others depending on what genre i'm obsessing over, but nothing for reference compares to the magazines:
EUROPEAN TRASH CINEMA, THE CHEESEPLANT, NOCTURNO, AMARCORD, GIALLO PAGES, etc.