OK pals, I guess I better chime in. You're right that this is a pet topic of mine.
covp -- my first response to you is that you're measuring the wrong thing. You say you have lots of volunteers but very low meeting attendance. And that's your challenge. I'll tell you that most folks would love the "lots of volunteers" part. That's way more important than meeting attendance.
Here's a column I wrote on that:
www.ptotoday.com/0805tim.html
So my first advice is: stop worrying about meeting attendance so much. All the gimmicks (raffles, principals giving teachers credit) in the world won't change the fundamental truth that PTO meetings are work/boring. We'd much rather have 150 at our next Family Reading Night (moms and dads engaging with their kids and the faculty, getting connected to the curriculum -- that's involvement!) than at a boring ol' PTO meeting.
As for other more general advice, two things:
1. You get the "unconnected" connected through great, welcoming, fun events. You bring 'em into school that way, not through your meetings or expecting them to be on your Board next year.
2. You increase the "core group" (the nuts like you who do lead and attend meetings, etc.) through personal interaction and recruiting.
The second follws the first, meaning: the better attendance you have at family events and the more welcoming you are, the more parents who will have a good thought in their head about your group and the better your odds of success in recruiting folks for your core group.
Good luck. With the volunteers you already have, it sounds like you're doing a great job.
Tim