I love 1-2-3 Magic by Thomas Phelan.
It's easy to read, easy to implement, and makes absolute sense. Although the book is aimed toward the 2-12 age group, we started the techniques (soft) at 18 months.
We don't have to yell, argue, justify, rationalize, over-discuss anything with our kid. We clearly state something like "no throwing toys - you could hurt someone" and then count him out. The counting gives him time to stop and think about his actions before deciding to repeat them or stop. If he makes it to 3, he goes into a time out. At the end of the time-out, we ask him "Do you know why you were in time-out?" and he'll give us the correct answer. After that he'll usually ask for a hug and say "sorry". He has learned that undesirable actions will result in removal from an activity. He has also learned to show remorse for when he has done something wrong BUT has also realized that, after the fact, we'll chat briefly about it and we reassure that we love him.
We have found these methods to be particularly effective with our now 2 1/2 year old child. We do not spend time wasting our breath over-explaining, pleading, justifying, begging our son to stop doing things. We simply state ONE TIME what he needs to stop doing and why he needs to stop doing it...and if he doesn't, every single time we follow through with the timeout. We have consistently followed this routine so now when he hears "one" he knows he is doing something he shouldn't be doing. RARELY do we get to "three".