Dear …
On behalf of __(The Board of Directors/etc.)__, please allow me to extend our gratitude to __(all of you volunteers/the Events Committee/etc.)__ for the tremendous work you all contributed to the __(type of event)__ this year. It was extremely well organized and superbly executed. Our compliments to each of you for a job well done!
Our __(type of event)__ is so important to us in that __(briefly describe the importance of the event to the organization)__. To have __(reached/exceeded our fundraising goals/ involved so many new donors and sponsors/etc.)__ was such a triumph for us. We consider ourselves very fortunate to have had a group of such capable volunteers to entrust a project of this scope to. The dedication that each of you demonstrated was outstanding. Thank you again for your tremendous contribution!
Sincerely,