It's always been kind of obvious to me, but apparently not to Tony Blair -- that greed doesn't make people happy. Psychologist Oliver James has explained this in a little more detail in his book "Affluenza" which came out a bit over a year ago, and now in a companion volume, which is a bit more academic, and which is called "The selfish capitalist: the origins of affluenza." Basically, James says that countries with a more social-democratic model of capitalism, such as Germany, have half the rate of depression and similar mental illness as the US, UK, and those that follow the "greed is good" philosophy of Blatcherism, so he concludes that a culture based on excessive greed and inequality is bad for people's mental health.
Basically, you'll probably find all the arguments in the works of Erich Fromm from the 60s and 70s already (e.g. To have or to be?), but if you need them spelled out in the modern context, take a look at these:
Affluenza (paperback edition) reviewed by Nicholas Lezard
The selfish capitalist reviewed by Madeleine Bunting
Selfish capitalism is bad for our mental health (an essay by Oliver James)