This letter thanks someone for going out of his or her way to help you.
1234, Main Street
Boston, MA 02123
07 April, 2005
<Recipient Address Goes Here>
Not everyone would have gone to all the trouble you did for me and I want you to know how much I appreciate it. It seems that you are always going above and beyond the call of duty. No wonder so many people are happy and proud to call you their friend. It was really wonderful of you to <what person did>, and I'll never be able to thank you enough.
Thanks again for everything you did. I look forward to having the chance to reciprocate.
encl: <List of enclosed items goes here>