Princeton University Press has recently published a book called The Princeton Companion to Mathematics. The chief editor of the book is Professor Timothy Gowers, who is a Fields Medal winner. It is a reference for every mathematician or anyone interested in Mathematics. Although world leaders in Mathematics have contributed to the book but, it will attract a wide range of audience.
It discusses almost all of the branches of present day mathematics, fundamental concepts of mathematics, biographical essays on famous mathematicians,influence of mathematics on other branches of knowledge etc. I believe it will provide a good introduction the subject to anyone.
I have tried some sample chapters from the book. Among them I found the Advice to a Young Mathematician very useful and stimulating. This chapter is contributed by world leading mathematicians like Michael Atiyah (Fields Medalist) and others.
Anyone interested may try some free chapters here.
WordPress posts on Princeton Companion may found here.