We all know about inter-library loans, and may all have used that service at one time or another. I mention it here only because it may not come immediately to mind when we are searching for genealogy sources.
We may look in the library catalog for a particular book, or we may look on line through Google Books, or eBay, or Rootsweb...to name just a few sources. But if we don't find the book locally or we don't find it digitized on line, how many of us forget that it may still be easily available through inter-library loan.
My personal experience with the service has been very rewarding. In one case I got a book about my family when I truly did not expect to. Only 18 copies of the book were published so I thought no library would part with it. I tried anyway and was rewarded by having the book to myself for a full month! And just this past week the Library at the University of Georgia came through with another book that had a limited distribution.
You can request an inter-library loan yourself using the computer (at the library or at home). Although this capability exists, the most sure-fire way to get the request made is to ask for assistance from a librarian.