Before we start searching for or playing with data, it helps to understand the copyright and licensing rules that apply to data and databases. 

The following two resources will give a useful introduction to copyright and licensing for data. Review each one, and then ask questions or make comments. 

1) The Guide to Open Data Licensing provides an overview of the different rules on copyright in data and databases by region. Different countries have different laws about data. http://opendefinition.org/guide/data/

2) The Creative Commons and Data FAQ introduces Creative Commons licenses for data, and explains how to determine what uses you can make of a particular database. http://wiki.creativecommons.org/Data.