For a sobering infographic display of income inequality in the United States, check out this video from YouTube channel politizane. For an opinion on the topic, delivered comedically by HBO's John Oliver, check out Last Week Tonight on the Wealth Gap. The Pew Research Center has a collection of articles relating to income inequality, supported by credible research and data. 

If you are interested in exploring income inequality globally, look into data on countries' Gini coefficients (also called the Gini ratio or index). According to the World Bank, the Gini coefficient measures income inequality by measuring how much the distribution of households/individuals' income or consumption expenditure deviates from a perfectly equal distribution. You can check your country's Gini coefficient at the World Bank website, and see how it compares to other countries. 

There are a number of important books discussing the wealth gap. Nobel Prize-winning economist Joseph Stiglitz's The Great Divide: Unequal Societies and What We Can Do About Them includes many examples specific to the United States, while Thomas Piketty's Capital in the 21st Century dissects the issue in both North America and Europe. If you would like to get involved in researching or narrowing the income gap, consider looking into the work of organizations like the GINI Project, UC Berkeley's Center for Equitable Growth, the Stanford Center on Poverty and Inequality, and Cornell's Center for the Study of Inequality.