These are effective examples of apology letters that have a personal or formal touch, it gets the message across that you are regretful of the incident and would like to make up for it
Apology letter to Customer for Billing Error
Apology for sending Incomplete Information
Apology for Missed Meeting
Apology to Co-Workers for Bad Behavior
Notifying Client that You are Out of Reach
Excuse or an indirect apology client for being out of reach
Apology Message for Not Returning Borrowed Item on Time
Making your friend wait for his precious thing, apologize now or feel his wrath!
Apology Letter: Returning an Item Too Late
Its been years, you almost own the thing you borrowed, don't you think its about time to return it?
Apology for the Delay Throwing off everyone's schedule? An apology is in order
Apology Notice to Client while Refusing Adjustment for Complaint
Chris Brown says Sorry through a letter
A Sorry Love Letter
Hurt someone very dear to you? Saying sorry is saying you love and value that person
Apology Letter after a Public Media Scandal
A well-thought out apology addressing the public after a scandal, most likely written by a lawyer or publicist.