I came up with some very similar ideas to the people above me: Steampunk (Wall clock made out of gears, Steam-powered TV), Nimbus (fluffy cloud couch, lightning lamp), and Origami (Crane chair, finger-fortune teller table). One special series could be the Turnip series: After buying, say, 500,000 bells worth of turnips total from Joan, she'll start bringing Turnip furniture. Each Sunday morning, one of the dialog options will be to ask for turnip furniture, at which point she'll tell you which item she brought that day. The furniture is random, but she has infinite copies, similar buying Mermaid items from the Island. My other idea for a set was the Novel series. A stack of books with the top one opened 90 degrees would be a chair, a bookcase with a false front would be a closet, things like that.