The Data and Story Library (DASL): (http://dasl.datadesk.com/) is a collection of data sets and related documentation (stories) that may be searched by data subject or statistical technique. A great place to visit for class examples.
Statistical Science Web: A portal for statistical science (http://www.statsci.org/)
Larry Winner's Miscellaneous Datasets: (http://www.stat.ufl.edu/~winner/datasets.html)
CSV format data for several R packages: (http://vincentarelbundock.github.io/Rdatasets/datasets.html)
The Chance Project: (https://www.causeweb.org/wiki/chance/index.php/Main_Page) has resources that emphasize using current news media as motivation for studying issues in probability and statistics. A highlight of the web site is the monthly Chance News (which now functions as a wiki), abstracting recent articles from newspapers and magazines with suggestions for pedagogical uses.
CAUSEweb: (https://www.causeweb.org/) the Consortium for the Advancement of Undergraduate Statistics Education, has helpful resources for teaching an introductory statistics course, including class examples, labs, homework assignments, data sets, cartoons, songs, jokes, and quotes. This site also houses information about the biennial U.S. Conference on Teaching Statistics and the Electronic Conference on Teaching Statistics.
The National Center for Health Statistics (http://www.cdc.gov/nchs/) The U.S. government’s principal heath statistics agency.
Fedstats (http://www.fedstats.gov) More than 100 agencies in the United States Federal Government produce statistics of interest to the public. The Federal Interagency Council on Statistical Policy maintains this site to provide easy access to the full range of statistics and information produced by these agencies for public use.
data.gov has more than 10,000 data sets in csv format (plus others in other formats)
publicdata.eu has more than 10,000 data sets in csv format (plus others in other formats)
World Bank has data in several formats, including csv an Excel
datahub has over 1,000 data sets in csv format (plus others in other formats)
The Gallup Organization (http://www.gallup.com) The Gallup Organization site give results from many of the polls they conduct. This site is good if you are looking for data dealing with proportions.