I'm putting this rec first, because no knowledge of canon is needed, and this story WINS ALL THE INTERNETS FOREVER:
Wild, Wild Zombieland (Lonesome Dove) - Even if you don't know Lonesome Dove, all you need to know is that there are cowboys and zombie cows. UTTER WIN.
The rest of the recs:
Breaking Patterns (Chronicles of Amber) - Oh wow, the author has got Zelazny's narrative style down, with all the twistiness and plotting and backstabbing and reluctant loyalty of the Amber royal family. If you like Amber, go read!
Carrying A Concealed Weapon (and other crimes to commit while being Adora Belle Dearheart) (Discworld) - A delightfully fun story featuring Adora Belle Dearheart and Sybil Vimes, with cameos from a number of others. Perfect Pratchett pastiche!
Make Time (Discworld) - EEEE VIMES! This is really awesome - perfect Discworld, with the best last line ever.
Three Ghosts. Well, One Ghost. Well, More Like Two People and A Bit Part For An Angry Spirit (Dresden Files) - Harry and Murphy at Christmastime, with ... a wee problem. This is hilarious and adorable; the author has totally got their deadpan snark down. And this is exactly the kind of totally FUBAR Christmas that Harry probably has all the time.
Rhyme Without Reason (Dresden Files) - Awesome long, plotty Dresden casefile story, with a perfect sarcastic Harry voice and lots of Thomas and banter.
Nothing Man (Ex Machina) - OH RICK. This is a wonderful story that makes the "oh Brian K. Vaughan, YOU TOTAL BASTARD" moment in the last issue so much better, without really being an outright fixit (it's too dark for that). It's not particularly a happy story, but it's a hopeful story, which is more than canon gave poor Rick, and it does perfect justice to a flawed-but-sympathetic character that I adored despite his darker side.
Mark in the Attic (Vorkosigan Saga) - I'm always on the lookout for Mark fic, and this is a neat little character piece, in which Mark gets a glimpse of his family's past.
Paying the Rent (Invisible Man) - Rather adorable buddyfic in which Darien and Hobbes discover that the missions in which they get shot at are the easy ones.
Making Up the Numbers (Red Dwarf) - Okay, if you guys are into Red Dwarf at all, you HAVE to read this. It's about Ace and "his" Lister and Kochanski, and looking for home across the dimensions. And it's just -- well, a lot more serious than Red Dwarf fic (understandably) tends to be, and a little heartbreaky, and just really wonderful.
And There Will Be Sorrow (No More) (Quantum Leap) - A different outcome for the last episode. I loved this so, so much.
Even Miracles (Quantum Leap) - This is a really neat look at Sammy Jo's life at the Project.
She Says It's Not a Love Song (But It Totally Is) (Yuu Yuu Hakusho) - (very background Shizuku/Yukina & Hiei/Kurama) Oh man, total blast from the past; I've been out of this fandom for so long that I'd forgotten a lot of the characters (it even took me about a third of the story to remember who Kurama was!). I always loved Yukina, though, and even though this story breaks up my OTP (Kuwabara/Yukina), it's done so mildly and respectfully that I didn't mind. And this is a lovely, long, slowly unfolding story about Yukina settling into the human world.
Are You There, God? It's Me, Little Rock (Zombieland) - I adored Little Rock in the movie and this is such a wonderful series of snippets from her POV! I love the look that we get of her relationship with her sister and how it changed during the zombie apocalypse (really!).
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