Firefly

Firefly's Glow Archive
A nice archive that became one of the centers of Firefly fic -- thre's very little on here that isn't at least readable. (Lots of slash; read it or read around it.)

Big Damn Zombies, Sir by Shrift
Shrift is a very cool person, and stories like this are just one of the many reasons. If the plot wasn't so utterly ridiculous (due to an equally ridiculous challenge), you'd swear you were watching an episode. The dialogue and interactions simply could not be more perfect. Go. Run. Now. Her I Have Gone Out is a lovely River piece, including the delight of seeing Serenity's crew through her mind. Shrift has a gift for making the best possible use of language, and this short story reflects that.
Cut Time Adagio by E.L.
Simon keeps the beat going. River scats. A quiet, lovely Simon piece that captures his voice, his heart and his relationship with his sister just beautifully.
Last Night at Sally Ann's by Maystone
Everything Maystone writes is excellent, but I love this one in particular. It's a romp, and an essentially pointless one at that, but who cares when it's this funny and sweet. Lots of 'shippiness happening here, all of it in character and with sparkling dialogue; the original characters are as cool and quirky as Our Loyal Crew. (For a more serious, deeply insightful character piece, read the outstanding Ghosts. For an all-around lovely River piece, go for Learning Curve.)
Pieces by Philomel
This is a Wash-centric piece, right after the events of "War Stories" and it rocks. Phil gets inside Wash's head effortlessly, and lets us see his life through his eyes. A little angsty, a little romantic, and very well done. For another lovely Zoe/Wash fic, try If All the World.
Space Pirates by Shanna
In this first in a four-story arc, Shanna presents us with episode-worthy dialogue and characterizations; while focusing on Simon, she gives us great Mal, Kaylee/Simon shippiness, and even some Mal/Inara. A tight plot and funny moments deftly mixed with the angst will have you reaching hungrily for the next stories (found in the same archive).

Words in Flight
It's always so much fun when an author you adored in another fandom wanders over to your new one. HawkMoth has never in her life written anything that wasn't excellent, but Turn of the Wheel tops them all. Welcome to Serenity's future; some of it's what you'd expect, some of it isn't, but all of it will touch you deep down. Simply wonderful. if you need something lighter afterwards, try her All Is Bright.

Aboard, About, Above, Across by jedibuttercup
"The Lady Tam was surely dressed for floor-twirling antics, and not the foufy-skirt type like what Kaylee preferred, nor the violent sort that had ended with Jayne on the floor, neither." Post-movie happiness.

Divine Manipulation of the Threads by Macha
Post-BDM, River's visions draw Serenity in another fight against the Alliance. Nicely plotted and characterized; at many points, it feels like watching a Serenity sequel. Entirely up to Macha's usual standards of excellence.

Embracing a Life of Crime by Macha
Wash's first involvement with crime and with Zoe. Unshakingly excellent Wash POV and a view of the start of his relationship with Zoe that is my new canon.

First Watch by Arwen Lune
River reflects during her first ship's watch aboard Serenity. Lovely little slice-of-life, and a really nice touch with River's voice. The last paragraph kills me. Post-BDM.

Gravity is Not Responsible for Your Fall by Viv
Inara in the aftermath of the Big Damn Movie. Gorgeous Inara voice, and wonderful moments with her and Mal. Call it an R for sexual situations and general grimness of circumstance.

If She Hadn't Been.... by Seanan McGuire
Mal and Inara, and all the reasons he knows he'll never have her. One of the most succinct and poetic summations of Mal and his torn feelings about Inara that I've seen.

Indistinguishable From Magic by kieyra
Post-BDM. Miranda wasn't the only secret River carries. Really, really awesome. KikiRec

The Habits of a Lifetime by Eleanor K.
Excellent Book backstory, beautifully written.

Mummys, Don't Let Your Babies Grow Up To Be Cowboys by Hossgal
I honestly can't summarize this except to say that it's short, it's funny and it's perfectly characterized. Go.

Of Kings and Hairy Feet by Tigerlady
In a boring piece of space, the crew of Serenity decides to pass the time by playing a childhood game -- Rings. Not quite crackfic, but close; the various members of the crew dividing up the roles of the Fellowship, and their ingenuity with props and playacting, are funny and often strangely appropriate. Mal's bemused participation is alternately hilarious and touching, when some roles fit just a little too well. (For an odd and entirely different, but very effective, counterpoint, try Of Kings and Hairy Feet (Draw Down the Stars Remix) by Sullen Siren.)

Scavenged by Salieri
GrimFic ahead, and that's not a warning I make lightly. An emergency repair for Serenity means Mal has to make a trip home. But the shopping trip becomes a dark and dangerous one for Mal and Kaylee, and the minefield is only the beginning. Excellent portrayal of everyone involved, the voices perfectly true to the show; Kaylee is valiant even in trauma, and her relationship with Mal is beautifully drawn.

Firefly @ Fanfiction.Net
I've said it before and I'll say it again: the drek-to-good stuff ratio is unreal, but Firefly has slightly better numbers than any other fandom.

Big Damn Heros by defender82
Wash is often underestimated as a character, but in this short, post-"Objects in Space" story and its sequel, it's up to him to bridge the gap between a worried Mal and a frightened Kaylee. Wash is wonderfully drawn, and his take on courage and heroism is sweet and true.
Choices by Tzegha
A novel-length Serenity-vs.-Alliance fic. When River is taken by the Alliance, Simon will stop at nothing to get her back, and the rest of the crew must choose sides. Plot, characterization, dialogue and atmosphere are dead-on throughout; this one is worthy of the name epic.
Listening in the Dark by Drewbug
Drewbug makes a poetic and shadowy trip inside River's head, where she has too much company and too much of it is dark. The language is utterly gorgeous, and River's voice is clear and heartbreaking.
Reliance by Roseveare
When Serenity crash-lands in an unfriendly place, her crew and her captain face a whole lot of bad choices. An exceptional fic that feels like watching an episode -- Roseveare captures the characters, the feel and the emotions of the show perfectly. There's a sequel that rocks just as much, and more is apparently on the way.
The Teaser Pony by Mikelesq
The crew of Serenity provides passage for horse with an unusual talent and a woman from Simon's past. The plot moves along quickly (if slightly predictably), Amelia is handled well, and you can almost hear most of the characters talking. Quite the fun read.
Two Gorram Days by Dyce
A series of events leaves an injured Jayne as sole keeper of River for, you guessed it, two gorram days. The resulting interaction is quite realistic and also quite touching; this is a very human Jayne who is still very much Jayne. The dialogue could have come from Joss' keyboard; I'm not sure the emotional connections could have. First in the very good Horseshoe Nail series; Dyce rocks in whatever fandom she writes. (This is eventually Jayne/River, but give it a shot even if that's not your cup of tea. It works.)
That Old Yeh Shen Story by Tara O'Shea
LJC gifts us with a sweet Kaylee/Simon romance that fits so smoothly into the Firefly 'verse, you'd swear you saw the episode. Gorgeous characterization on the duo and Mal and Inara in particular, but everyone gets their chance to have a little fun onscreen. By turns sweet, poignant and hilarious -- absolutely a must-read.