There are many datasets available online for free for research use. Some of them are listed below.

If you’d like to have some datasets added to the page, please feel free to send the links to me at yanchang(at)RDataMining.com. Thanks.

• The R Datasets Package:
  see a list of data in R datasets package with the statement below
  > library(help="datasets")

• Frequent Itemset Mining Dataset Repository:
  click-stream data, retail market basket data, traffic accident data and web html document data (large size!).
  See the website also for implementations of many algorithms for frequent itemset and association rule mining.

• ACM KDD Cup:
  the annual Data Mining and Knowledge Discovery competition organized by ACM SIGKDD, targeting real-world problems

• UCI KDD Archive:
  an online repository of large data sets which encompasses a wide variety of data types, analysis tasks, and application areas

• UCI Machine Learning Repository:
  a collection of databases, domain theories, and data generators

• CMU StatLib Datasets Archive

• GeoDa Center:
  spatial data

• Time Series Data Library:
  a collection of about 800 time series drawn from many different fields

• EconData:
  A source of economic time series data from Inforum, at the University of Maryland

• UCR Time Series Data Archive:
  data for time series classification and clustering

• Free GIS data at Geoscience Australia

• Datasets on Social Network:
  http://cnets.indiana.edu/groups/nan/truthy
  and
  http://www.public.asu.edu/~mdechoud/datasets.html