My earlier answer was focused more on elementary school. Many of the things Jewel suggested, however, have been done at my kids' secondary school, specifically--
Teacher/staff appreciation lunches
Front office assistance (making copies, answering phones, greeting visitors)
Grounds beautification (weeding, planting)
Coordinating and hosting after-school activities
Also, setting up speakers on health/safety/parenting issues (such as internet safety, teen drinking, drug abuse, gang activities, etc.) can work well for parents of older kids.
Tech Teacher-
That's fabulous. There are so many wonderful programs that don't involve fundraising. In fact groups that focus too much on fundraising have a tougher time getting parents involved. Looks like you have some good ideas from Jewel, mum24kids, & Sheri.
Here are links to programs mentioned in their posts & some links with some other ideas: