Leaving Serenity by Celli is a stunning Out of Gas missing scene that beautiful illustrates exactly what Serenity means to Mal.
Tetchy by debchan really captures both Simon and Jayne, and in addition to being hysterically funny, is also pretty damn hot.
Opaque by Northlight is a lyrical dissection of Mal and Inara's relationship. The stylised nature of the piece works better than expected, and it's an interesting insight into Inara in particular.
Battleground by maystone is a very sweet missing scene from Objects in Space, as Mal helps Kaylee deal with her guilt over her inability to fight in either War Stories or Objects in Space. First-time writer maystone has a great handle on Mal and Kaylee's relationship, and Mal's voice in particular rings true.
A Modest Proposal by Grey Bard is an atmospheric and quirky look at how Wash was hired.
The Filament Series by Lemon Lashes is determined to make me a Wash/Simon fan. Lemon really fleshes out Wash's character in particular, giving him shades of grey and demons of his own that are only hinted at one the show. Not to mention, all the stories handle Wash's marriage to Zoe incredibly well. If you've got a few hours to spare, the series is well worth your time.
Safer by juli is a nice little alternate version of the Mal and Simon tag of Safe which delves a bit into the characters' interactions. Short, sweet, and insightful.
A Companion's Lot by Mara Greengrass is a lovely little slice of Inara's life.