Despite my recent X-Men reading bias, I have not gone completely mono-fannish, but these few AU and xover recs would have been lost amidst the large number of X-Men recs, so I decided to stick them in an extra post.
Criminal Minds/Harry Potter
In Darkness, by Mhalachai. Gen, Aaron Hotchner. (ca. 3,700 words)
The premise here is that Hotch is squib who left the magical world, but his son has magic. I really enjoyed the squib perspective here.
Eagle of the Ninth
Fighter, by PlaneJane. Slash, Marcus/Esca. (ca. 65,300 words)
This is for the movie I haven't watched, and it is a modern AU on top of it, so it read somewhat like original fic, but the whole setup worked well for my kinks: Namely, Marcus is an undercover police officer who infiltrates a slave-trafficking ring that organizes cage fights. He stops Esca from being killed in a fight and thus gains a slave.
SGA
Almost Human, by esteefee. Gen. (ca. 30,200 words)
This a robot!Sheppard AU, with a Rodney who doesn't trust the AIs. I was wary of the fic due to all the author warnings, because breaking of trust between my favorite characters (and mindcontrol not written as kink) risks running into my partner betrayal squick, but I like the cyborg/robot trope so I gave it a try and this worked well for me overall with the way it resolved things.
Sherlock
Strangers, by cj_ludd18. Slash, Sherlock/John. (ca. 34,000 words)
Another robot AU, this one with robot!Watson. I wanted to punch Sherlock a lot for being a jerk in this, but that rather fits with his characterization, so it's not really a complaint.