This article called "The Leadership Gap" was one of the strongest inspirations for this website. There is a lot of very interesting information about how and why confidence effects women.
Lean Inby Sheryl Sandberg contains invaluable information about female leadership within the workplace.
The media plays a major part of in creating the confidence gap. Miss Representation is a movie that discusses these issues and poses potential solutions. Great movie!
In my Women & Leadership class at Gonzaga University, we used Gendered Lives by Julia Wood as a textbook. It is very well-written and is very easy to read (honestly, it doesn't sound like your average textbook). It gives great overviews of gender issues within the United States.