Love letters: a romantic gesture sure to delight.
Apologies: say sorry gracefully with a letter from the heart.
Condolences: a sympathetic letter in a time of grief
Complaints: a well-written letter increases your chance of getting results
Round robins: share your news without sounding boastful
Just a look at her blog shows that any letter she writes will be both beautiful and interesting, unless of course you ask for a dull letter. Which, while not being against the law, would be a shame.