Besides Kenneth Boulding's 1971 HOPE article, Mark Blaug's 2001 Journal of Economic Perspectives piece, "No History of Ideas, Please, We're Economists," is also very helpful, I think, in persuading people of the usefulness of a course in the history of economic thought. Sometimes, one is better able to deal with problems in current economics by reading the past originals, I have found. My examples would include (a) the notion that there is a paradox of thrift, (b) the alleged neutrality of money in the short run, (c) that we can represent the classicals by a vertical aggregate supply curve, (d) that we can represent modern money (M1, M2, etc) by a vertical supply curve (with respect to the rate of interest), and (e) that there is such a thing as autonomous government, business, or consumer spending (in a closed economy) that drives a meaningful expenditure multiplier. James Ahiakpor