You can read all of her fics here on AO3 (and here's her masterlist on LJ), and you should. (Well, I can't vouch for any other than the Merlin fics, but I'd imagine that they're just all awesome.) I'm going to highlight a few of my favorites below. I'd list them all, but that seems like cheating. She's one of those authors who consistently produces things perfectly to my liking. I'm even considering reading her non-Merlin fic just so I have more of her stuff to read.
[#23 - Dew Point] Title: Dew Point Fandom: Merlin Pairing: Merlin/Arthur Rating: NC-17 Word Count: ~58k Link: http://archiveofourown.org/works/425397 Author's Summary: Arthur Pendragon is as popular and successful as a sixth former can be. He hasn’t quite figured out his future yet, but it’s going to be brilliant, he’s certain. At least until some daring stranger on a cool motorcycle topples his world upside down on the first day of school. Modern magical AU.
This was her recently revealed hs_merlin fest submission. It was one of my top two favorite fics of the fest (right up there with Gamut). Like everything she writes, the story and world she created are rich and detailed. The story is from Arthur POV, so there's a ton of (necessary) mystery surrounding Merlin. He shows up out of nowhere, looking all dark and sexy, and immediately catches Arthur's (and everyone else's, too) eye. There's a nice twist on the traditional Sophia story thrown in, Merlin's a badass (in a million ways), both he and Arthur are smart as hell, and the whole story is just sexy. She mentioned in her repost on her LJ that she was originally considering making this a whole Verse, and that would be lovely, because there are lots of places I'd love to see this story go.
[#24 - A Change of Pace] Title: A Change of Pace Fandom: Merlin Pairing: Merlin/Arthur Rating: NC-17 Word Count: ~54k Link: http://archiveofourown.org/works/426567 Author's Summary: The one in which Arthur works in finances and his suits are various (two) shades of grey, Merlin works in advertisement and has no boundaries whatsoever, Morgana drinks rum, Mithian stages a coup, Agravaine is aggravating, and Elena's house is amazing. Also, Andy Warhol is mentioned in vain, and Arthur and Merlin fall in love in Victorian era style.
This was originally a kinkmeme story, but since I rarely read anything over there (is it horrible that the format drives me spare?), when she reposted this a few weeks ago, it was completely new to me. New and awesome. Arthur is emotionally stunted and trying to please Uther; Merlin works in marketing and is amazing and creative and whirls his way into Arthur's life and turns it completely upside down. Like all of Kianspo's stuff (mostly--see below for one... two, really, that are more on the sad side), there's an awesome balance of funny and drama/angsty, and it's all very smart and sharp. When I got to the end of this story, I honestly cried for no reason. Just because it was over, I guess--that's how much I loved it.
[#25 - Time Forward] Title: Time Forward Fandom: Merlin Pairing: Merlin/Arthur (and Gwen/Arthur, but have faith) Rating: Teen and up Word Count: ~23k Link: http://archiveofourown.org/works/340682 Author's Summary: While still at uni, Arthur Pendragon meets two people who become his best friends. He falls in love with one of them... but marries the other. This isn't his story to tell; it's Merlin's. And Merlin will always remember that he met Arthur first.
This is... well. It's complicated and sad and made my heart ache a whole lot. Shattered it, really.
Merlin is imperfect. And he fucks up. Arthur isn't exactly perfect either. Things don't look good. But if you just have some faith....
Hmm, now I'd kind of like to go reread this again right now, even though it'll keep me up until 3 a.m. and make me cry a lot.
[#26 - Pockets Full of Stones (Lay Me Down)] Title: Pockets Full of Stones (Lay Me Down) Fandom: Merlin Pairing: I don't know? Merlin/Gwaine? Little bit of Merlin/Percival. At its heart, it's a Merlin/Arthur, even if non-traditionally. Rating: Mature Word Count: ~3.6k Link: http://archiveofourown.org/works/269494 Author's Summary: “You can’t,” Gwaine says in a pained voice. “Merlin... True or false: if Arthur had so much as a single gay bone in his body, a single gay hair on his head, even, you’d be married to him by now?”
This fic, this fic. Sigh. I feel so badly for Gwaine. And Merlin. And Arthur. Kind of everyone. It's kind of the story of a relationship that isn't all that healthy and how all other relationships in their worlds can (and cannot) fit around that one. It's short, but it'll give you enough feelings for a story four times as long.
She also has another amazing story, Same River Twice, that would have made this list if I didn't have something else planned for it for a subsequent 100 Things post.
ETA: I forgot to mention this--she also makes really good recs and has them posted to delicious. Definitely worth a look!