Many public libraries are supported by their Friends of the Library groups. One of their prime fund-raising ventures is the book sale. Such an event can be used to liquidate older versions of books that can be valuable to your genealogical research. Older atlases may be useless to a library or a donor, but may be invaluable to your work. Reference books; language dictionaries; almanacs; local, state and national histories; and other books may supplement your reference collection at a tiny fraction of the price of new books. Check with your library as to whether they or other libraries in your area sponsor book sales.