Skeptic's Annotated Bible / Quran (Koran) / Book of Mormon
The Bible is an important piece of literature and cultural icon of western society. Even if you don't ordinarily read works of fiction, I encourage you to read the Bible to be a well informed citizen.
Even the King Jame's Bible is easier to read than Chaucer, and is no more difficult than reading Shakespeare. As in the case with Shakespeare it is handy to have an annotated copy to point out historical and cultural vagaries.
The Skeptic's Annotated Bible is an excellent resource to keep handy while you are reading the Bible and get confused by the alternate versions of events and the multitude of self-contradictions.
While not as important as western cultural icons you may want to read the Quran and Book of Mormon with annotations as well. It pays to be prepared for your next visit by the door-to-door Mormon missionaries.