I absolutely adore the series This day in "lettres" by The American Reader journal. The concept is simple; identifying and reprinting letters that have been exchanged between intellectuals from the past on a daily (almost) basis.
This is one of the cutest ones I've read, sent to Victor Hugo by Juliette Drouet, his mistress at the time.
"Good-morning, my dear little beloved, my darling little man. You told me so definitely yesterday that my handwriting was hideous, and my scrawl nothing but a horrible maze in which you lose both patience and love, that I hardly dare write to you to-day, and it would take very little to make me cease our correspondence altogether"