I recently borrowed a book from the library called Hidden Sources Family History in Unlikely Places, by Laura Szucs Pfeiffer. The book is basically a listing, with resources, of many places researchers might not think to look when researching their family.
Some of the hidden sources are: Admiralty Court Records; Apprenticeship Records; Bankruptcies; Centennial Publications; Deeds; Fire Insurance Maps; Homestead Records; Licenses; Necrologies; Occupational Records; PERSI; School Censues; Street Indexes; Urban Guides; and Works Progress Administration.
I thought Motor Vehicle Registration Records was an interesting source I had never considered. Apparently there are records for both driver’s licenses and motor vehicle registrations you can locate for some ancestors.
This is a must have, or at least a must see, book for every family historian.