I stumbled on Grid Republic today! [link]

Its a pretty neat concept. You can volunteer your excess computing power by joining the computing grid for various worthy projects. Amazingly the process to get started is very simple. Just enter your name, email address and pick a password.

On the next step you pick the project you want to help out and finally download and install the application.

You can check on the progress of the projects at any time. The screenshot above shows the image being generated on my machine! Just amazing!

There is a status page too on the website which shows the progress of all these projects and the computing power they use! Give it a go!