As introductions to film noir, you can’t go past these two books, which are immensely readable and entertaining:
The Rough Guide to Film Noir (2007)
A great introduction that covers the genre from early German expressionism to the latest neo-noirs, and highlights the movies to look out for.
Film Noir by Alain Silver (2004)
A general overview of film noir covering its most important themes with many rare stills. Among the films covered are: Double Indemnity, Kiss Me Deadly, Gun Crazy, Criss Cross, Detour, In A Lonely Place, T-Men, Out of the Past, The Reckless Moment, and Touch of Evil.