USA Science Festival in Washington, DC
Austin Science Festival in Austin, TX, I'm closer to this one and will probably go see it. They will have a virtual laboratory on the Wii. Would LOVE to bring that back to the classrooom!
San Diego Science Festival in San Diego, CA, had to list this one. My best friend from college works here for the Navy as an Electrical Engineer, applying science every day.
Satellite events around the nation: Satellite Event Directory