If All the World by Philomel in another in the growing sub-genre of epic recountings of the untold story of Zoe and Wash's courtship. And it's fabulous, and makes me want to marry Wash.
A Taste of This by Jane St. Clair is a series of five things that never happened, little slivers of elseworlds that illuminate Simon's character through different lenses. Not to be missed.
Centripetal Motion by Rachel is a delicate Kaylee/Inara vignette just packed with a rich level of detail.
In Heaven There Are No Walls by Pablo is a gorgeous little Simon vignette that picks apart Simon's fears and worries and hopes with a deft hand. Really lovely.
Patience by hossgal is a nifty little look at the de-facto mayor of Whitefall, post-Serenity.
Battle Scars by Piper is a post-Objects In Space scene featuring Simon and Jayne that captures the adversarial nature of their relationship quite well--and strikes me as very easily believable. I'd also love to see a flip-side version from Jayne's POV someday, especially considering the events of Ariel.