Dear …
RE: __(Name of Project/Event)__
On behalf of __(name of organization)__ please allow me to extend our deepest gratitude to you for speaking at our __(name of event)__. As you know, it was very important to us that we convey the right message at our __(reason for event – i.e. fundraiser/unveiling/etc.)__. I must say that we were absolutely delighted that your speech carried it off so __(well/beautifully/etc.)__. Thank you!
We greatly appreciate all the support you have given to our __(type of project/event/organization)__. You have been so instrumental in helping __(us move this project forward/making this fundraiser successful/etc.)__. From the __(type of support given)__ to __(type of support given)__, we remain grateful to you.
The dedication you show to __(name of community)__ is admirable, __(Name)__. Your personal involvement in this community really is a great benefit to us all.
Sincerely,