This letter is a courteous, professional way to thank an interviewer for considering you when you did not get the job you were looking for. You never know when a company that rejected you will offer you a job six months later because of a courteous letter.
1234, Main Street
Boston, MA 02123
04 April, 2005
<Recipient Address Goes Here>
I was naturally disappointed when I heard that you had filled the position of <position> with someone other than me. But since that is the nature of business, I wanted to write and thank you for your courtesy and your professionalism during our <interview/interviews>. You made a sometimes uncomfortable process easy and pleasant.
I wish you good luck with the individual you did hire, and I hope that when another appropriate position becomes available, you will consider me. Thank you.
encl: <List of enclosed items goes here>