Personal favorites: A Noguchi lamp. "It's also a sculpture that is warm, comforting and very flattering."
What's essential: An empty 1950s Danish Modern wooden bowl and a comfortable ottoman.
The tip: Blossfeldt photogravures--great in any decor. In a traditional room, their stark photo-realism makes it feel modern; if they're hung in a very modern room, they add a late-19th century botanical feel.