I think Buffy people would also like Amy's Cold Kiss.
I was just thinking about Firefly last night and how I generally don't like space or westerns, but I like Firefly, and when I try to think of something like it I come up with nothing. I think people in general would think of recommending other space-type things.
Maybe the Expanse novels: also a small crew of a ship with space adventues. (James S.A. Corey.)
The Rocinante crew doesn't map exactly onto the Serenity crew, but they're strongly reminiscent.
I think of the Vorkosigan novels as their own fandom, so I can't easily map them onto another one. Doctor Who, maybe?
I think Buffy people would also like Amy's Cold Kiss.
Oooh, I concur.
As I note in my Hilbrow piece today, Game of Thrones fans would like Fritz Leiber.
In fact, if you've ever thought, "Damn, they totally should've hooked up Brieth and Arya to tromp around and get into trouble and snark at each other" then that's basically a gender-swapped version of Fafhrd and the Grey Mouser.
How about the Vorkosigan novels for Babylon 5 fandom?
I kinda want to say Leverage.
You should read Lumberjanes if you are a fan of...anything?