I liked Toddler Taming by Dr Christopher Green. Ignore the heading - it's not really about "taming" your toddler, just good commonsense stuff as to the whys and wherefores of toddler behaviour and some practical, sensible ideas on how to deal with behaviour (also looks at other typical toddler issues such as toilet training, food etc). It's also humourous and doesn't take itself too seriously.
Same as well as Toddler Tactics by Pinky McKay.