I recently came across this. I didn't know about this but I thought I would share for those who haven't yet heard of it. In summation, a satellite is being sent into space as a time capsule. It contains many things from our present day and everyone on this earth is given a chance to write something to be place inside it. It will return in 50 000 years.
wikipedia for more info. : http://en.wikipedia.org/wiki/KEO
If you want to contribute something click on "Your Message" to write something and it will be added to the time capsule (uncensored!)!
I forgot to mention, you have a lot of time to think of something. The capsule isn't being launched until 2010 or 2011. Sorry, a correction: the deadline is Dec 31, 2009