In one of the schools I worked at, the parents had a car wash. Staff left their car keys in their mailboxes in the office with a piece of paper with their licence plate/car make and model on it. Parents set up outside the school with buckets, hoses, sponges, and a radio and washed cars all afternoon. The parents who did it said they had a great time--and I loved driving home a shiny, clean car.
Another appreciation gift they gave us was paying for our water cooler for a year. They gave each staff member a cup with a lid and a note saying that the PTA would be providing the water service.