This best-selling book by British researchers Richard Wilkinson and Kate Pickett makes the case that high levels of income inequality lead to a wide range of health and social problems in modern wealthy societies (click here to see an excellent presentation these ideas by Wilkinson). The book is full of charts like the following (all based on peer reviewed research)
Surprisingly, these health and social problems do not correlate with average income
The authors theorize that inequality produces all these problems by increasing status anxiety and damaging community solidarity, producing stress and distrust which in turn lead to health problems and crime. The last section of the book is devoted to ideas for reducing inequality. I found particularly interesting their call to encourage alternatives to corporations, such as coops and ESOPs - both of which are much more common in the UK than in Canada. An organization called The Equality Trust has been set up to promote awareness of these ideas and push for policy changes and you can view more charts and learn more on their website.
The Spirit Level has had a positive influence on the policy debate in the UK. The leaders of both the Conservative and Labour parties have spoken favourably about it. If these ideas were more widely known in Canada, it would move our politics in a better direction too.