April 12, 2012
Dear Mr./Ms. Bossname,
I am terribly sorry to be sending this notice to you, especially after having only been employed for (number) months/weeks, but I must resign from my position here at (company,) effective (date.)
I pride myself on being a loyal and dedicated employee, and I regret putting you in this position after the wonderful opportunity you have offered me. However, (personal reason/relocation, death in the family) means that I can no longer work here. I hope you understand, and that I have not inconvenienced you too much.
Thank you again for all of your help and consideration.