Does anyone know any good ideas for a school fundraiser?

Sell something people want. Your market doesn't have to be other students. You could sell yardwork or housecleaning services. Teams of two or three could knock on doors to offer and schedule the work, then do it on a later day. See if you could set up a hot dog "stand" or sell baked goods outside a major store or mall.

Many companies offer fundraiser programs. Tupperware, Home Interiors, Little Caesar's Pizza Kits, Cookie Dough companies, wrapping paper, etc. Find a mail order company that you can set items for and they will give you part of the procedes.