Dear Mrs Lowe
This letter will confirm my resignation from the position of XYZ. My last day of employment will be Friday February 3, 2012 which includes the required two weeks notice period.
I have really enjoyed working at ABC Company but I now find that I have an opportunity to further develop my career in keeping with my long term goals. It is largely due to the valuable experience I have gained working for ABC that I am now able to pursue this growth opportunity. I have appreciated the opportunity to develop my skills while working with such a positive team. I would like to thank you for all your support and encouragement over the last X years/months.
I wish you and the company the best of luck for the future.
Sincerely
Your name