There are a lot of wonderful plants, but my all time favorite is Myriophyllum matogrossense. It is a feathery stem plant, sturdier than Cabombas, grows in just about any light level, and in medium to high light, quickly grows to fill its space. It’s easy to trim, becomes thicker when trimmed, and looks great! M. matogrossense grows in the pond (even overwintering in Atlanta some years) and fish love to use it for spawning, with the fry using it as hiding spaces. It will grow floating, but looks best panted in the substrate (imho – as if there were really any h imo). It’s also a nice bright green color, though if the light is high enough the growing tips will be slightly pinkish looking (of course be sure to supply little sunglasses for the fish if your light levels are that high).