While Ronon is a Runner, he goes to a world that he knows is deserted, one that's known as a Runners' World, and is horrified to find a kid there: deaged Xander, who can't or won't speak for whatever reason. Ronon tries to send him to/drop him off at an inhabited world, but he won't go, just follows Ronon around and occasionally kicks wraith ass. And refuses to leave his axe behind even though he can barely lift it.

Somehow, Hermione and Luna meet before Hogwarts. And Luna has all sorts of books with proof that all of her creatures exist, so of course Hermione is convinced...

Supernatural/Pride and Prejudice, although with only P & P characters and OCs (and, I guess some of the longer-lived Supernatural characters, just not any of the humans). Set in/around P & P times. The reflex might be to do it as an AU, but I think I personally prefer it not to be.

Elizabeth Bennett (or Darcy) is a BAMF Hunter, eventually almost a legend, despite...well, everything. Mostly gender. How did she get into Hunting? How did she get to be so good? How do her interactions with other Hunters go? What's her life like?

Crazy alternate universe, where males can only reproduce with males and females can only reproduce with females, but either pairing can produce children of either gender; this pattern extends to any species which does not reproduce asexually. Give careful consideration to social changes--e.g., like IRL each couple would need at least one partner to work to support them, back through history, so gender discrimination is not going to have ever been like it is or was here; also, everybody is gay is the only thing that makes sense here.

Protagonists are a straight couple in the modern day, extremely aware of how lucky they are to be living in a time when it's legal and to some degree accepted for them to be together and hoping that someday soon it will be legal for them to get married.

In TV, books, and movies, it seems like every detective/PI/cop deals with the big crimes--murder, rape, art theft, etc. So what about one that's about cops/detectives who deal with minor crap, or are traffic cops or something? With the focus being a lot more on the people rather than the cases. Stick in a supernatural element, preferably a lot more understated than in other shows: each of them has a supernatural secret and doesn't know their partner's secret (though it doesn't drag out for too long; eventually they find out because otherwise they just look stupid), but most of their cases are normal, mostly boring cases, and their supernatural secrets only occasionally affect their lives. Put a limit on how often they have to draw their guns, and how often the supernatural causes more than minor irritation, and stick to it.

It's the equivalent of the '60s in Urban Fantasy World. The race issues are mainly between werewolves and vampires (and humans?) rather than blacks and whites.

MC is a police detective, but they also secretly run/rule the city's supernatural community. Most of the time it works out, but now they're working hard on an important case, and having to deal with important stuff going on in the supernatural community. Are the two connected? Will she be able to deal with both at the same time? When will she ever be able to get some sleep?

A vampire in some sort of anti-addiction program.

Somebody who has the kind of powers that are basically "you must fix this problem or your life will continue to be disrupted" gets so jaded that he stops doing it because he wants to do good, stops being outraged at horrible things, etc.

Hey, you know what would be a fun crossover? Dexter/Journeyman. Several possibilities: Dexter travels through time (and let's just say he solves problems a bit differently than Dan and Olivia do). Deb travels through time, and finds out about Dexter. Dan has to help Dexter, and may or may not find out about him.

MC develops powers of a type that can't be proven (psychic visions or something, not telekinesis or anything easy to prove) and starts hiding them from everybody. Only later do they learn that their sibling has had the same power for longer, and has been hiding it all along as well.