Books
It depends what sort of information you want - "Stanley Nowak - Ferrari On The Road" has general information on road cars and a long list of chassis numbers, other books are more model specific, such as John Starkey's - Ferrari 250 GT berlinetta TDF, Ferrari 250 GTO by Bluemel and Pourret, or John Godfrey's Ferrari Dino SPs, whilst some are just books of pretty pictures with no chassis numbers, history, etc.
I now have sixty Ferrari books, my first purchase being Dream Machines FERRARI by Godfrey Eaton, my last being the previously mentioned Ferrari 250 GTO by Bluemel and Pourret. Think before you buy and choose a book which gives you the information you want. Looking back now there are a few books bought in my youth that are not specific enough for my current interest.