depending on if you specialize or are a broad spectrum collector the answers might be different
*but my first choice for reference is :
"bayonets from jantzen's notebook"
its got line drawings and a few B&W photos , but its set up by country in alphabetical order , itemized by model with noted series if it evolved ,
it cross references other sources ,
"My" narrow scope is both US and Commonwealth from 1880-1970s ,
**for most of the US i recommend ;
gary cunninghams , 'american military bayonets of the 20th century' ,
he has excellent line drawings identifys models and markings in depth , including scabbards , mfgrs , contracts , and foreign use
and also published 'bayonet points' on franks t's site
www.usmilitaryknives.com that site also has bill porters 'reports' and other great info ,
**for my commonwealth i recommend ;
skennerton & richardson 'british & commonwealth bayonets'
has great B&W photos , some line drawings and super coverage of patterns , markings , mfgrs , prototypes , experimentals , scabbards , frogs ,
hope this helps , there are a number of internet sites i could link as well , im sure others have their favorites in their focus areas as well