Mark your calendars: this year's Software Freedom Day is September 20 (the third Saturday in September). If you're looking for an occasion to help out with the spread of free and open source software, that's a great one.
An annual event since 2004, SFD is designed to be both a celebration of free software's successes and a public education effort to help further its acceptance. It has a fairly impressive sponsor and partner list, including Google, Canonical, Sun, the FSF, and more. Participants are encouraged to form local "teams" of free software advocates, to work together on projects. To check whether there's a team near you, try the team page on the SFD wiki.
Last year, over 300 teams participated in SFD. It's getting late, but not too late to join, or even form, a team. What can a team do? Pretty much anything: hold an installfest, release software, organize a new user group, write an article for the local paper, hold a public lecture...it's up to the participants. The only real requirement is to sensibly demonstrate the advantages of free software.
While it's safe to pronounce SFD a success at this point - the hundreds of teams involved get the word out to many thousands of people - there's clearly room for more. If the vision of a world running on free software appeals to you, it's time to pitch in and do your part.