The U.S. Census Bureau is a great place for all sorts of data on the citizens of the United States. You can find details as varied as the length of their commute, ethnic and racial breakdown, income, marital status, age and sex breakdowns, just to name a few. There are two sources for this data, one free and one that you have access to through the library.
In addition to searching for demographic data from the Census, there are number of sources of polling data. Polling and market research focuses on particular topics, such as people who attend particular events, consume foods, have particular opinions, etc.
Want even more data? This web page breaks down all the various data sources we have access to at CU by subject.