"The Jewish Holidays" by Michael Straffeld

This book is an encyclopedia of information on all the Jewish holidays.  While it is compiled by one man, there are copious notes in the margins from other commentators.  From sukkot to shavuot to yom kippur and more, readers will understand what traditions are for those holidays.  There is even a section on understanding where the dates come from and how the cycles of the moon play into that.  In terms of pictures, there is a good balance of images to show things look like.  For example, a seder plate and a sukkah are not left to mere words--there are illustrations.  What I enjoyed most about this book is that it explained where traditions come from with respect but left it up to the reader to decide what is important.  So, while someone may decide to opt out of a certain ritual, they will at least know its significance.