Variety of data sets:

http://mathforum.org/workshops/sum96/data.collections/datalibrary/data.set6.html

http://exploringdata.net/datasets.htm

http://www.middlesexcc.edu/faculty/Jeanne_Osborne/pages/excel_data_files.htm

US Census Bureau

http://www.census.gov/main/www/access.html

http://www.census.gov/dataviz/

World Bank

http://data.worldbank.org/

Weather History for Los Angeles (Precipitation, Low/High/Average Temperatures, etc):

http://weather-warehouse.com/WeatherHistory/PastWeatherData_LosAngelesIntlArpt_LosAngeles_CA_January.html

United States Department of Labor (multiple data sets for Average Prices):

http://data.bls.gov/cgi-bin/surveymost?ap

NBA Attendance and Ticket Prices:

http://mathforum.org/workshops/sum96/data.collections/datalibrary/NBA.Att.Prc.XL.zip.xls

NBA Kobe Bryant Statistics:

http://www.basketball-reference.com/players/b/bryanko01.html

Median Annual Income by Level of Education (2009):

http://www.infoplease.com/ipa/A0883617.html

Smoking and Cancer:

http://lib.stat.cmu.edu/DASL/Datafiles/cigcancerdat.html

Crimes and Crime Rates by Category and Crime for California listed by County (and other related links):

http://oag.ca.gov/crime/cjsc-stats/2010/table1

http://www.fbi.gov/about-us/cjis/ucr/crime-in-the-u.s/2010/crime-in-the-u.s.-2010/tables/10shrtbl02.xls

Major League Baseball Average Salaries by Years:

http://www.cbssports.com/mlb/salaries/avgsalaries

MLB Los Angeles Dodgers Statistics:

http://mlb.mlb.com/stats/sortable.jsp#sectionType=sp&playerType=QUALIFIER&statType=hitting&page_type=SortablePlayer&season=2011&season_type=ANY&sportCode='mlb'&league_code='MLB'&split=&team_id=&active_sw=&game_type='R'&position=&sortOrder='desc'&sortColumn=avg&results=&page=1&perPage=50&timeframe=&extended=0&last_x_days=&ts=1342743026555&tab_level=child&click_text=Sortable+Player+hitting&elem=%5Bobject+Object%5D

Immigration Statistics (Various tables on immigration):

http://www.cbssports.com/mlb/salaries/avgsalaries

Hockey Statistics (Pittsburgh Penguins):

http://penguins.nhl.com/club/m_seasonselector.htm?cb=m_standings&season=20112012&type=division

Genetically engineered varieties of corn, upland cotton, and soybeans, by State and for the Unites States (2000-2012:

http://www.ers.usda.gov/data-products/adoption-of-genetically-engineered-crops-in-the-us.aspx

Median Household Income by State (1984 to 2010):

http://www.census.gov/hhes/www/income/data/historical/household/2010/H08_2010.xls

List of most expensive paintings:

http://en.wikipedia.org/wiki/List_of_most_expensive_paintings

Oil Production:

http://lib.stat.cmu.edu/DASL/Datafiles/Oilproduction.html

Health Care in Cuba:

http://blog.geoiq.com/2008/06/03/dataset-of-the-day-health-care-in-cuba/

Population and Census Costs by year:

http://www.census.gov/prod/2002pubs/pol02marv-pt5.pdf