Testnet
On Testnet, it is quite easy to obtain free ether, as there are so called "faucets" where you can receive free test ether.
- https://test.ether.camp/: Click on "Get free ether" in the menu bar.
- https://zerogox.com/ethereum/wei_faucet
You need separate accounts on testnet (Morden) and the Main Network (Homestead). Don't confuse them ;-)