Here are some middle school level books that are good for teaching social studies. These three are novels about topics that would be good to use in reading circles, whole class, or student selected parallel reading:
Tough Times by Milton Meltzer, topic Great Depression
Dawn and Dusk by Alice Mead. This book is about Iran/Iraq conflict from the perspective of a child living in Iran.
Lawn Boy by Gary Paulsen is a good story that teaches about economics. It is about a boy who starts his own business. Kids love Gary Paulsen.
A good resource for finding books for specific topics you are teaching can be found on the National Council for the Social Studies web site. Each year the council publishes a list of books by topic and level that it recommends for classroom use. Also try searching the documents on enotes for a plethora of information.