I haven't seen one of my favorite stories recced so far, so now is my chance!
Dangerous Liaisons (1998):
Checkmate is sly and smart. It's a prequel to the movie detailing how the Marquise de Merteuil and the Vicomte de Valmont first became entangled. They are written beautifully here - calculating, yet drawn to each other.
I've also enjoyed these stories:
A Study in Emerald:
Lex Talionis is a crossover of amazing proportions. It's written
perfectly - somber in tone, true to both Holmesian and Lovecraftian traditions, well characterized - and then the crossover comes in, and you say "How can this work?" And then it works, and WOW. Make sure to read to the end.
Blackadder:
A Living Princess features the little princess bride from the first Blackadder series growing up and coming into her own.
Addams Family:
Violet was a lovely surprise. Macabre, colorful, and very sweet.
The Outsiders:
broken knife broke my heart. The author captured the characters and the hard lives they lived, and the Johnny and Dallas relationship was perfect.
Raising Hope:
See Sabrina Write is a letter from Aunt Sabrina to little Hope, advising her to be happy, because we all have our Grocery Paloozas to learn from and rise above.