Biblical references telling us we should be angry

Overheard on a Christian Radio station this morning: > We all know that Jesus said if we are angry without cause, we are in > danger of hellfire, and that the Bible tells us to be slow to anger. > But did you know that there are situations in which the Bible says we > are supposed to be angry? Unfortunately, I couldn't listen to the program being advertised, so I'll ask it here. Where, in Scripture are we told to be angry, and about what is it OK to be angry? What is the "cause" that is acceptable if we aren't supposed to be angry "without cause". Please include Scripture references. If applicable, links or comments from official/recognized teachings would be a good addition, particularly if the Scripture reference could be interpreted multiple ways.