Red Thai Hibiscus: lemony, grape-leaf-like flavor, good mixed with other greens, good for sautéing, yummy as part of the greens in a smoothie, flowers in late summer followed by red calyxes which can be harvested for a delicious red tea/drink. Annual.
Amaranth: this is the same plant that amaranth seeds come from, the leaves are edible too, younger leaves for raw eating, bland flavor so best mixed with other greens, older leaves better cooked (a common weed: redroot pigweed is an amaranth plant, and is completely edible as long as not sprayed with yard chemicals) Annual. Reseeds.
Salad Burnet: this green is pretty enough to be in a flower bed, it has a delicate cucumber like flavor, with small frilly leaves in pairs on a stem, red flower stalks. Perennial. Reseeds.
Orach: also known as mountain spinach, comes in several shades of red, magenta; tastes very spinachy, but is also very ornamental and could grow in a flower bed. Annual. Reseeds.
Strawberry Spinach: a small plant with triangular, toothy leaves; good, simple flavor; would work well as a flower garden filler or edger plant; later in the summer, red berries form which are also edible and are said to have a mild raspberry-strawberry flavor. Annual. Reseeds.