Entirely subjective. Consists of good stories I happened across that never claimed much screen time in the ol' feature box:

Funatics by Baal Bunny

-While Luna/Celestia sisterly love fics are hardly uncommon, this one's take is both mature and delightfully original. I say "mature" because it tackles head-on a fact that few in this fandom care to admit: that Luna and Celestia are, assuredly, not equals. Not in forgiveness, patience, or any of the other things that count for a good sister and leader. Luna's acceptance of this, and pursuit of a brief "Kindness War" with her sister make up this story, filling it to the brim with quiet humor and gentle wisdom.

Dusk Falls by NorrisThePony

-A Celestia-focused story taking place before Nightmare Moon, it is almost two stories in one: Celestia vacations to small town Equestria (the titular Dusk Falls), leaving the nation in her sister's hooves. There, oddities lead her to investigation, which leads her to a Lovecraftian conspiracy long in the making. At the same time, Luna's efforts to rule Equestria alone have been less-than successful, putting their already-strained relationship to the test as Luna comes to assist. Both parts shine, creating a brooding story of mystery rife with personal conflict.

I'll probably add more later, as I sort through my faves bin.

4937810
Feel free! Some group is better than no group.

4937810
Can confirm Funatics for good story. Will have to read the other!