Boston.com has a great interactive chart of the American Community Survey.  The chart shows different characteristics (median household income, median age, percentages of the population with a certain ethnic background or educational level attained, etc.) and allows you to select Massachusetts cities and towns that have a population over 65,000 for comparison.

I recommend comparing Worcester and Springfield (or Worcester, Springfield, and Lowell) on any level, or the average household income differences between Worcester, Springfield, Cambridge and Somerville. 

Watch out — it’s extremely addictive!