Australian electronics engineer Dave Jones has published a great video on YouTube showing how you can help SETI search for alien radio signals using your Raspberry Pi.
Don't worry if you don't have a Raspberry Pi and would like to get involved, you can download the software for many other devices (Windows, Linux, Android and Mac).
Go to: http://boinc.berkeley.edu/download.php to download the software. When your computer/tablet etc is idling, BOINC harnesses your computer's spare CPU power to process scientific data.
More detailed information can be found here: https://en.wikipedia.org/wiki/Berkeley_Open_Infrastructure_for_Network_Computing
Who knows, your computer may be the one that proves we are not alone in the universe!