Census.gov The main resource for demographic data is the U.S. government. Here are some nice starting places.
Statistical Abstract of the United States Statistics on the social, political, and economic organization of the U.S. Demographics on birth rates, death rates, marriages, divorces, and education are available.
American Time Use Survey Measures the amount of time people spend doing various activities, such as paid work, childcare, volunteering, and socializing.
Pew Social and Demographic Trends project studies behaviors and attitudes of Americans in key realms of their lives, including family, community, health, finance, work, and leisure. The project explores these topics by combining original public opinion survey research with social, economic, and demographic data analysis.
Consumer Expenditure Survey Consists of two surveys, the quarterly Interview Survey, and the Diary Survey, that provide information on the buying habits of American consumers, including data on their expenditures, income, and consumer unit (families and single consumers) characteristics.