The art of the thank you note is not practiced as much as it once was, even though they always make the recipient happy. Mental_floss has collected some of the best thank you notes ever from the archives of Letters of Note. For example, here's a note Neil Armstrong sent to the Extravehicular Mobility Unit engineering team.
You'll enjoy the others just as much, if not more. Link
To the EMU gang:
I remember noting a quarter century or so ago that an emu was a 6 foot Australian flightless bird. I thought that got most of it right.
It turned out to be one of the most widely photographed spacecraft in history. That was no doubt due to the fact that it was so photogenic. Equally responsible for its success was its characteristic of hiding from view its ugly occupant.
Its true beauty, however, was that it worked. It was tough, reliable and almost cuddly.
To all of you who made it all that it was, I send a quarter century’s worth of thanks and congratulations.
Sincerely,
(Signed) Neil A. Armstrong
You'll enjoy the others just as much, if not more. Link