Here is a letter that I use:
Thank you very much for all your assistance with planning our Campus interviews at (name of College).
Your expertise in handling the logistics, the meeting arrangements, the multimedia presentations, coordinating travel, and in organizing the event were greatly appreciated.
I thought you would like to know how we fared at the event:
Number of students seen =
Number of applications received =
Number of candidates invited for first interview =
Number of expected placements =
I really appreciate your help and I am sure we will be contacting you for your assistance with our next event.
In the interim, if I can provide you with a recommendation or if there is anything else I can do to assist, please don't hesitate to ask.
I hope the above helps.
Please feel free to amend as per your own requirements.
13th June 2013 From United Kingdom, Barrow