Bitcoin faucet
Bitcoin faucets are sites to earn some bitcoins for free. They usually needs address entry and captcha filling. You can revisit faucets every given time to get more.
First faucet was operated by Gavin Andresen, however it is not functioning as of Jan 30 2013.
For Testnet there exist different faucets that is working which gives out coins for people who want to do tests on the Testnet.