There is one place in the Internet where you can get some Bitcoins instantly and absolutely for free. This is Bitcoin Faucet site. It gives away to each new visitor 0.001 Bitcoins. You may ask your bitcoin only once for each IP address and Google account. To get 0.001 BTC you need to enter your bitcoin address and authorize with your Google account. Then you will get transfered coins in your Bitcoin wallet almost instantly.
If you are a developer and test your Bitcoin-related soft you also can get some coins in Bitcoin TESTNET branch.