The classic set customized to be chocolate brown, the cabin set (of course), the modern wood set, the mushroom set, the alpine set customized to be dark brown, the campsite set, the cabana set and maybe the green set.
As for individual pieces, you could use a fireplace in just about every room, the coffee cup you get from the cafe, the tea set, a basket chair, a bistro table, a box shaped seat, casablanca lilies, cypress plant, pothos, cat tree, lily record player, autumn leaf chairs, bonsai trees, a bird house, writing chair and writing desk...
I could go on forever :U
Moridb will probably help you out a lot.