Favorite one-shot?

I'll start

http://www.fanfiction.net/s/8065437/1/Petunias-in-the-Summer

Summary: "When Severus Snape makes an unexpected appearance on the Evans' doorstep, it throws Lily's differences from her family into sharp relief."

I really like this author, but this one is my favorite.

What are some of your all-time favorite oneshots?