You have until Dec. 31, 2006 to come up with something enlightening to tell future generations. Specifically, the future generation of intelligent life that'll be toiling around this hunk of landfill in 50,000 years. Yes, in other words, cockroaches (youtube link, thanks Bryce).
A cuddly-feely group of scientists, humanitarians, and artists have convinced The People With Money that humankind circa 2006 needs to send a message to what They believe will be humankind circa 52,006 by way of a satellite called KEO (thanks Andy). Lucky for us, this a democratic group of optimistic futurists; they'll allot 6000 uncensored characters (~ 4 typed pages) to each of us joes, with which we may express ourselves to the roaches yet to be born. Click here to pollute the minds of earthlings, the next generation.
KEO is nowhere near the cosmic equivalent of tossing a message in a bottle out to sea. This winged(!) satellite, to be packed up at the end of the year and launched into orbit in 2007/8, will hold a human genome-etched diamond that encases a drop of human blood, and samples of air, water, and earth. If that's not sci-fi enough, the re-entry plan should win you over: upon passing through the earth's atmosphere, KEO will produce an artificial aurora borealis. Check out this page for other technical highlights.
I'm a fan of their data encryption plan, personally. Our collected messages to the future will be encoded on radiation-resistant glass DVDs. And just in case there aren't any DVD players around in 50,000 years, the KEO team is including a detailed diagram for how to build one, laser reader and all. Let's hope Radio Shack is still around, eh?