There is a large selection of books on Newark history, culture and architecture. Some of them can be located by using NJIT Libraries online catalog ( type "Newark" as a subject or as a key word). Books in digital format can be found via the Digital Archive of Newark Architecture on the Books page. Some of them are scanned and saved in PDF fromat while others are made available via the Google books site.
There are also links to catalogs of other libraries which are instrumental for finding books not owned by the NJIT.
You can find more books available online by searching Google Books
Perhaps the majority of information on Newark architecture can be found in articles. Many of them have been digitized and made available on the archive page Collections/Articles, many more can be found by searching various indexes and databases. Although, indexes unlike full-text databases will provide citations only, you should not underestimate them. Avery Index is an invaluable tool for finding information on architecture, urban planning, as well as on specific buildings and architectural images.
You can find more articles by searching Google Scholar