Word of mouth is fantastic. Also, kids wearing T-shirts to school with your logo on it is good. If there are any community festivals, show up and show out in a good way. By that I mean do things like set up a booth and hand out "freebies" and brochures about your gym. If you have anyone who is willing, maybe have a group of people put on a little performance. I broke concrete blocks all summer downtown to draw a crowd and let my training partners cut cucumbers off me with machetes, walked on glass and did all kinds of weird stuff, just to draw a crowd. haha...You don't have to go that far. Anyway, back on track, if you have a friend who is a teacher, this is good. Get him or her to wear T-shirts with your logo on it to school and to maybe leave your business cards in the office or the workroom/lounge.
Those are just a few ideas. I actually work in a school. I'm a teacher and I'm in the process of establishing my own martial arts school. I've been hoofing it doing all those things I said above. haha...handing out brochures, attending festivals, doing the facebook thing, designing t-shirts and logos and stuff and I'm getting ready to hit up the newspapers and radio. Hopefully, I can get a spot on a couple of talk shows. Anyway, those are just a few ideas.