Panel Study on Income Dynamics (PSID)
This dataset is "one of the most widely used social science data sets in the world" and has been used in more than 2,000 publications and working papers. The PSID is a "longitudinal study of a representative sample of U.S. individuals (men, women, and children)" began in 1968 and continues to today. It started with a representative sample of 4,800 families and has grown to more 7,000 as original participants have had families on their own. "At the conclusion of 2003 data collection, the PSID will have collected information about more than 65,000 individuals spanning as much as 36 years of their lives. ... The central focus of the data is economic and demographic, with substantial detail on income sources and amounts, employment, family composition changes, and residential location. Content of a more sociological or psychological nature is also included in some waves of the study." In addition, there are often supplemental surveys of the participants. Considerable effort is made to ensure that the data across the years is consistent.
Their Data Center offers a straightforward way to retrieve the data and codebooks in a variety of formats. Other types of information on the project is available as well.