456, X Street, Y Avenue
[Subject: Normally bold, summarizes the intention of the letter] -Optional-
Dear ANDREW HALL
As you are aware I have been looking for a new job for a few weeks now. I thought though that you should be one of the first people to know that I have been successful in gaining a position at a new company in York. I know that my successful application was helped in no small amount by the professional reference that you provided on my behalf. The company looked extremely favorably on my resume after receiving your reference.
I am writing this note to thank you for the time you put in to give me the reference and your support has been much appreciated, as has your continued encouragement. Many thanks for all of your assistance and everything that you have done for me.