There really isn't anything that hasn't been written about. But I would like to read a book about history to the locals of a given region. Not about govt or major events but about daily life with LOTS of pictures of the places they went about, their homes/transportation, popular items, trends, and of course the people themselves.
Other things I like to read about are funny little stories about people's lives. Nothing too outrageous but just enough to give me a giggle when I'm feeling blue.