July 27th 20XX
Mary Crabby, CEO
XYZ, Inc.
100 My Way Ave.
Washington, DC 20002

Mary:

This letter serves as my written notice of my resignation effective July 9th 20XX. My last date of employment will be July 27th 20XX.

Thank you for giving me the opportunity to work for XYZ, Inc. In my time here I have learned valuable skills that I will utilize throughout my career. I hope that I have been a positive member of the team here, and have made substantial contributions. I appreciate all that you and XYZ have done for me over the last 4 years, and wish you good luck in the future.

Please let me know what I can do to make this transition as smooth as possible as I begin this new chapter in my career.

Sincerely,
Ima Champion

Don't forget... after each interview, be sure to immediately send a "thank you" letter, or you won't even be considered for the next round.