I have been researching knots lately too. I don't have any book recommendations but check out the website Animated Knots by Grog.

From what I have read over various forums and websites, the recommended knots to learn (for general purpose applications) are these:
Square knot
Bowline
Two Half hitches
Taut line
Clove hitch
Figure eight
Sheet bend
Prusik

I want to stress that I'm not an expert at knots, these are simply the knots that I am working on learning myself.

-Robert