November 17, 2014
Dear Mr./Ms. Bossname,
An exciting opportunity has come up that will allow me to continue my career path in (field), which as you know has been a longtime desire of mine.
Unfortunately, this means I must tender my resignation with (company), effective (date).
Thank you very much for your support during my time here. (Company) is a wonderful, forward-thinking company, and I will truly miss working here.