Come Out and Play is an awesome annual street games festival that started in NYC in 2006. Seek 'n Spell was part of the festivities in 2009, and the event was a total blast! Last year there was an SF offshoot, and it's back again with the main weekend of games happening November 4-6. Submissions for games are now being accepted, so if you've got a game you'd like to run during the event please submit! Just make sure you get it in by September 15. If you're not a game designer but still want to be involved, they're also looking for volunteers to help out. Otherwise, be sure to mark your calendar!
* Disclosure: I'm helping organize the SF event this year.