I wrote a few letters to the editor back in my younger days, and two of them were published.
My first letter appeared in the June 1984 issue of Isaac Asimov's Science Fiction magazine. Asimov was my principal idol during my teenage years, and I subscribed to his magazine for about a decade. Needless to say I was (and still am!) very excited to see my letter in his 'zine and to know that he had read and responded to it.
I also had a letter published in the December 1984 issue of DC's Star Trek comic book.