Robert A. Heinlein : A Reader's Companion

Rating:
Summary: Just essential
Review: This is probably the best reference about Heinlein's works that's ever been written. One of the best thing about it is that it's complete and very well organized, so that you can find whatever you're looking for in a few seconds, very handy.
Since I've bought it I've consulted it hundreds of times, I couldn't do without it.