The SETI@Home program lets you use your spare clock cycles to help process data for SETI, the Search for Extraterrestrial Intelligence. Clicking their logo above will take you to their web site, where you can find out more and even download the software and help out.
The software downloads data gathered by antannae pointed at distant stars in hopes of finding patterns amongst the background noise of the universe. It is thought that intelligent life will likely evidence some sort of pattern discernible to us here on earth.
On 23 December, 1999, I got a very strange pattern on my SETI@Home screen. The folks at SETI are quick to point out that not all discernible patterns are necessarily caused of extraterrestrial intelligence. The pattern that appeared in my data, however, was almost distrurbing. I'm not exactly sure what to make of it, but check it out and see for yourselves: