I have a bookcase full of genealogy research books such as "The Hidden Half of the Family" by Christina Kassabian Schaefer, "A to ZAX, A Comprehensive Dictionary for Genealogists & Historians" by Barbara Jean Evans, and an old worn copy of "Migration, Emigration, Immigration Principally To The United States And In The United States" by Olga K. Miller. However, my favorite go-to resource is the classic "Map Guide to the U.S. Federal Censuses, 1790-1920" by William Thorndale and William Dollarhide.
The Map Guide includes maps for all states, broken out by census year, and also depicts the changing county boundaries overlaid onto the current county lines. In addition, it gives availability information for each census year. For example, I am looking for my third great grandfather, John Gannan, in Monmouth County, New Jersey, b. 1826. I can quickly tell by looking at the New Jersey map for the 1790 - 1820 census that the Federal Census was lost for all counties except extant for Cumberland County in 1800, and so it will be a waste of research time to search for any type of Federal census information for John's parents.
Another example is Hocking County, Ohio. I have early pioneer families there, and by reviewing the Ohio map for 1800, I know that part of the current county falls into the Washington extant census; in 1810, the Federal census was lost for all counties except Washington (which is now much smaller); and that today, old Hocking County records might be held in Fairfield County, Athens County, or Vinton County.
The Map Guide by Thorndale and Dollarhide has been a valuable resource tool, and is one of very few books I will actually take along on research trips. If you haven't seen the book, chances are your local library has one. It's been around since the late 1980's, but it's a classic that I highly recommend for any genealogy home library.