These are the libraries that I use quite often for my genealogy.  They may of use to some of you.  I always recommend looking for state and local libraries or archives where your ancestors were born, lived, married, and died.  There is a lot of information at these libraries that is not necessarily on the Internet.  You may need to call and/or go visit them.

Abraham Lincoln Presidential Library

Allen County Public Library

Arlington Heights Memorial Library

Chicago Public Library

Cleveland Public Library

Illinois State Archives

Illinois State Library

Library of Congress

McHenry Public Library District

Mid-Continent Public Library

Newberry Library

New York Public Library

Wisconsin State Archives