There is also a Philosophy Bites issue in which Alex Voorhoeve argues what is bad about inequality, but that is more on a theoretical level. (see Three issues of Philosophy Bites)
Richard Wilkinson and Kate Pickett took on the practical approach and collected data from all over the world and compared the social fabric of societies where equality is greater to those where inequality is greater, as far as wealth is concerned. On Big Ideas you can hear a lecture in which Wilkinson brings that point with a stream of examples home. What is interesting to find out is that not only is inequality bad for the poor. In societies where there is greater inequality there is more crime, more psychiatric disorder and people are less happier and live less longer and this affects the rich as well.
More Big Ideas:
Dan Dennett: what should replace religion?,
Needham about China,
The Reluctant Fundamentalist,
Ayaan Hirsi Ali and the quest against Islam.