Collections of digitized reference books can provide many edited sources with valuable background information about your research topic. Reference books entries usually refer to more detailed sources and can also suggest terms you can use when searching for books and journal articles. Links to four collections are below.
Growing collection of electronic reference books -- dictionaries, encyclopedias, bilinguals, almanacs, handbooks, atlases, and directories.
A continually growing collection of electronic reference books -- dictionaries, encyclopedias, almanacs, handbooks, atlases and directories. There are bilinguals, general and specialized reference books, and all can be searched from one interface. See the title list on the website.