One book that I've read recently that encompasses all religions is Religious Literacy: what every American needs to know--and doesn't by Stephen Prothero. It proposes that religious studies should start in junior high and high school. To back this up he gives his students at the religion department at Boston University a test--one in which they resoundly fail. Most in this religious studies class can't name all four Gospels. The book itself is more of a clearly written history of religious literacy with a large glossary of religious terms at the end a la Cultural literacy : what every American needs to know by E.D. Hirsch, which my 11th grade English teacher used to test us every week on everything from Moby Dick to Ophelia. In fact, one school in California has a mandatory religion course that Prothero believes the rest of the country should model.
I really like the idea of both of these books, with lists of terms to memorize and learn from (hey I aced 11th grade!), although their has been criticism of this method of lists. Who decides what is on the list of what is religious or cultural literacy? And just because you know the names of the four gospels, does that mean you understand the meaning and context of them? One thing is for sure: I've got some studying to do.