This is the first real book I read on Judaism. I had been reading for months random things online and this book made organic connections between all the facets of Judaism for me. Except for the chapter on Kabbalah, it is a fantastic introduction to Judaism. I suggest skipping chapter five if you're new to Jewish study.
Jewish Literacy by Rabbi Joseph Telushkin
One of the best survey books of Judaism out there. Every rabbi recommends it both for converts and born Jews. It's just fantastic. It's set up with 1-2 page chapters of hundreds of Jewish topics: Bible, history, ethics, holidays, life cycle events and more.
This is My G-d by Herman Wouk
This book was written quite some time ago. It is very Orthodox in its perspective. Wouk also writes novels which is reflected in this book: very story like.
The Choosing by Rabbi Andrea Myers
BEST BOOK for any prospective convert to read. Do it. Now.
Their Hollow Inheritance by Michoel Drazin
This book turned out to be very different than what I was expecting. But it is a book attempting to counter Christian missionizing to Jews, showing that the verses from the Hebrew Bible that Christians quote proving Jesus as the messiah are actually taken wildly out of context. It was recommended on some website for converts who are leaving Christianity. Chances are you probably don't subscribe to Christianity if you want to convert to Judaism, especially if you're on my blog. I just don't like that websites assertion that converts from Christianity need to read this. We can think for ourselves in figuring those things out. However, it was still an interesting book if you are interested in Christianity's use of the "Old Testament."
Entering the High Holy Days by Reuven Hammer
A lot happens during the High Holidays. I read this book because the High Holidays are not something I grew up knowing about. A lot happens at the services. Also, since they are the most important time of the year for Jews I figured I should get really acquainted with them before experiencing them. You should buy this book or at least take notes because there is no way you could remember all the facts that comprise this book.
To Be a Jew by Rabbi Hayim Donim
Another survey of Judaism, written from an Orthodox perspective. I like this book because it has a lot of prayers in Hebrew so you can get some practice. The chapters on Kashrut (dietary laws) are really good.
Pledges of Jewish Allegiance: Conversion, Law, and Policymaking in Nineteenth- and Twentieth-Century Orthodox Responsa by David Elleson and Daniel Gordis
This book analyzes how the Orthodox Jewish community got to their very strict standards of conversion. It's insanely interesting but the conclusions are somewhat disheartening.
There is No Messiah and It's You by Robert N. Levine
This is no introduction to Judaism book. Do not read this unless you have a solid basis of Judaism and Jewish history. You are expected to know a lot of Jewish theology and philosophy. Also, this book isn't necessarily rejecting the idea of a Messiah. Its main points are "Don't wait for someone else to fix the world" and to trace the evolution of the ideas about the Messiah. It's an excellent book.
To Life: A Celebration of Jewish Being and Thinking by Harold S. Kushner
Another survey book of Judaism for the prospective convert. Hoping this is the last survey book...