I think what most people would want to see are "generic" people packs. Like a "Fantasy Set" with some generic warriors, wizards, elves, dwarves, orcs, different townsfolk, and the like. Or a "Sci-Fi Set" with futuristic fighters, bodysuit armor-type, different kinds of aliens but all the same "race". Those kind of packs would ge eaten up like hotcakes
All you need would be basic animation:
Standing
Walking
Running
Attacking while standing still
Attacking while running
Taking Damage (flinching)
Dying
Of course you can add specific animations afterwards for special attacks or abilities, but those basic ones are generally all that's needed. Sometimes you don't even have to use all the basic ones... you may not want the townspeople to fight at all so you don't need thier attack animations... always good to have, though
As for models for a scene, once again it all depends on what you want. For a "Fantasy Set" I would go for buildings of different sizes and shapes of stone and wood, catapults, stone towers and wooden towers, weapons racks, barrels, crates, wall hangings, loose swords and arrows (to lie around the scene as if a fight just occured), dead bodies. Or for a "Sci-Fi Set" you would want extra ships of differenet shapes and sizes for humans and aliens, ruined//blasted machinery, alien eggs not hatched/hatched, different planets (ringed, ice, desert, etc), cluster of astaroids, single asteroids.
Those are just some ideas... personally I'm only interested in Fantasy/Sci-Fi so those are the ones I would be interested in. My advice would be to pick a theme, do the pack, then pick a new theme, do the pack, and repeat as neccesary. As your collection grows you can add new sets to existing sets (IE "Fantasy Set II with new models") and build your library up.