There are two celebrations of science coming up you might be interested in.
1) Galilean Nights is a worldwide event sponsored by the International Year of Astronomy 2009. The idea is simple; get as many professional and amateur astronomers to show the skies to people from October 22 - 24, 2009. That's it! Just get people to come outside and look up. You don't need to be part of an organization to do this either; if you have a 'scope, then invite your neighbors to check out Jupiter, Albireo, Mizar and Alcor, or M13. If you do participate, make sure to register your event so the folks at IYA can keep track.
2) The Quantum to Cosmos festival is sponsored by Waterloo, Canada's Perimeter Institute. They want to teach everyone quantum mechanics, an idea I think is great. They have lots of info online, including a couple of cute short movies; Alice and Bob in Wonderland actually looks like it can give kids some good insight into QM. The festival lasts for ten days in October, so check it out!