Well-styled shelves can make a room. I love to mix and remix the arrangement of books and art and ceramics on my own shelves.
Small paintings are an easy choice for the art.
Paintings with a wider edge stand on their own edge without a need for leaning or an easel (or a nail in the wall). They're light to move around, so you can mix and match and mix again. Move them in seasonally, or re-arrange when your books or dimensional pieces change.
'Looking In’ is the perfect pop of color on a wood shelf. An original painting, 10x10", it's still available in the store: