There are a lot of Government Web sites that have made the data that they collect and compile freely available to the public. The licenses that data has been released under are described on the following Pages:
ODC Public Domain Dedication and License (PDDL)
Open Data Commons Open Database License (ODbL)
Open Data Commons Attribution License
If you are considering starting a project using that kind of data, you should read the Open Data Handbook, which provides a lot in the way of details, and much more information is available on Data.gov, including a broad overview of different types of topics that data is available about, including:
- Local Government,
- Public Safety,
- Science & Research.
There’s some interesting discussion of Licensing, openness of data, and attribution in a blog post from the Open Knowledge Blog, titled Open Data: Openness and Licensing.