Best FF That Manages to Be More Touching Than Every Word Tolkien Ever Wrote: Love, All Alike, by Sheila. The Lord of the Rings. We spend so much time thinking about those who sailed into the west. What happened to the ones who were left behind? Tolkien never seemed too interested in those that stayed in Middle Earth; Sheila fixes his lapse with this wonderful snapshot of Merry and Pippin at the end.
Best FF That Is Excellent Therapy for People Still Upset about Order of the Phoenix: Say His Name, by jjtaylor. Harry Potter. (I suppose technically you could consider this pre-slash or implied slash, but in that case you could consider the canon to be implied Remus/Sirius slash.) OotP introduced us to a brand new Harry Potter sub-genre, which I think of as five stages of grieving fic. I'd say this lovely little story is firmly rooted in stage four, depression. I suppose we'll have to wait for the next book to see acceptance fics.
Best FF That Demonstrates Why You Should Always Have a Martian Handy: Stillpoint, by Sarah T. Justice League animated series, and you don't need to know anything about the canon to enjoy this story. An extraterrestrial alien seeks a human alien on reservation land - hell, there's enough marginalized and excluded people in this story to start a union. It's no surprise, then, that this fic is all about belonging.
Best FF That Made Me Absolutely Detest C. S. Lewis for Several Minutes: Girls Grow Quicker Than Books, by Kyra Cullinan. Narnia series. This story deserves every superlative at my command. It isn't just FF; it's biting commentary on the Narnia books and on Lewis' treatment of his female characters. The only other story I've seen that did this kind of thing is Jane Yolen's "Lost Girls," which won a Nebula award. And "Girls Grow Quicker Than Books" is better than "Lost Girls." Read this - it's short, it's wonderful, and it will completely change the way you think of Narnia and Aslan.