Under what conditions is it morally justified to break the law?

In what sort of cases would you endorse civil disobedience? In your answer, think about 1) how you would define the idea of an unjust or immoral law. Would you agree with St. Augustine that ‘an unjust law is no law at all’? and 2) what cases (if any) would count in your view as legitimate uses of civil disobedience? For some examples, take a look at the Wikipedia article on civil disobedience.

http://en.wikipedia.org/wiki/Civil_disobedience