I find that one of the simplist forms of thanking volunteers is a note card with a written message. It really shows that someone made the effort to recognize the time each volunteer gives.
Sometimes I have worked with the staff to have a volunteer appreciation luncheon or one year we did desserts. The teachers really liked the idea that they could say thank you to parents that really go out of their way for the school.
I have also worked with the teachers to have students create thank you notes or artwork. That was probably the most talked about by parents... they loved it.

I was wondering how you folks thank volunteers. As you know these family nights would not happen without our wonderful volunteers. Do you do something to recognize them? 2 nights ago we had our annual carnival and I have had 3 parents tell me they were put off by not recieving a thank you on the night in question and will think twice about volunteering next time. This causes me great concern as we barely had enough volunteers to cover each shift. Some even did not show or called in sick. Luckily we utilize the High School leadership class to fill in the gaps. One of the teachers and I also scheduled or Middle schoolers to make sure we had all stations covered. Honestly, we never would have pulled it off without those who showed up and those who were willing to cover additional shifts for no shows. I think it would be wonderful if we could have an appreciation dinner at the end of the year (not for profit). We would invite all families, but the volunteers and their family eat for free. What do you all think? Any other ideas?