Some of you know philomytha's work already; she's written quite a lot of good Vorkosigan fic, and I've recced a few of them before, including a crossover with Doctor Who (Electric Blue, in which Eleven takes Amy and Rory to Barrayar). She's done it again, this time with a novel.
Aral Vorkosigan's Dog is Simon Illyan's perspective on Shards of Honor. I wasn't sure I'd enjoy it, because honestly those "prequels" are the ones I've read only once and never gone back to; I'm much more fond of Miles and Co. But this is brilliant, working within all the insane politics of the time, showing the damaged emotional tangles between Aral and Vottuyer and Prince Serg and Bothari (and all their poor military underlings). I love her Aral, who is so clearly the man we see in later stories, but more fiery and much more like Miles eventually becomes. And Illyan, who is young and intellectual and analytical, and finds himself slowly drawn into loyalty to this man, over and above his duty. Warnings for violence, sexual assault and non-con/rape, about at the level of the book it's based on.
It is currently a WIP, but the entire fic has already gone through beta, and she's posting at the rate of about a chapter a day.
Then we have Guerrilla, by Glishara
When a new Cetagandan invasion strikes at the heart of Barrayar, leaving much of the government dead and Barrayar itself cut off from the greater galactic community, it falls on Ivan Vorpatril and the team he can assemble to keep hope alive and form the new Resistance. AU for Diplomatic Immunity.
This is amazing, you guys. Everyone is in character, even in the extreme aftermath of what would have happened if Diplomatic Immunity had gone very, very wrong. It's Ivan's story, completely, but with seeds and shards of many other people and storylines that we've seen in previous books, and a lot of Illyan, Alys Vorpatril, and Duv Galeni. Emotionally staggering, and very exciting. Warnings for graphic violence and deaths of major characters from the series. (AU, yes, indeed.)