But, wait, maybe you happen to have some computers over a network. If this is your case, it's a good idea to think about Yadra.
Oliver Schulze wrote us about his tool that enables you to render your Blender animations over a network on many computers, which stands out for its easy setup and stable operating.
It's open-source and written in Java, so there's support for any operating system around. You can get info on installation and use on the wiki. One of its cool features is the web-based management tool, to take track of your brand new render farm.