BJ Penn's book of MMA knowledge.

Brazilian Jujitsu Theory and Techniques by Royler Gracie.

Encyclopedia of Brazilian Jujitsu by Rigan Machado.

If I had to choose just one, I would probably go with the Encyclopedia of Brazilian Jujitsu, but they are all worth the money.
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin