Another book I have been reading recently is the 8th Habit by Stephen Covey.
Although it may sound a bit cheap to first write a book about the 7 habits of highly effective people, and then go on to write a book about the 8th habit, I think his subtitle (from effectiveness to greatness) makes sense.
The key of this book is finding your 'Voice' and helping people to find theirs.
What he means by this is explained in this youtube video.
If you are interested, you can find the The 8th Habit: From Effectiveness to Greatness here.
In het Nederlands is het boek ook hier te krijgen..