Re: After BSG, B5, Firefly & Ds9... what's left?
Check out The Adventures of Brisco County Jr. It's Bruce Campbell in a sci-fi western. Since you liked Firefly, you might enjoy this show.
Also, going back a few decades, I also recommend Wild, Wild West.
"They have to help the viewers let go. Firefly did a movie to wrap things up. Buffy the Vampire Slayer continued on as a comic book. Heroes gradually lowered the quality season by season until we were grateful it ended.” - Sheldon Cooper