dwarf hairgrass would work. anubias nana 'petite" would as well. in fact, if you plant any of the anubias close to the surface, they will eventually break the surface and start to grow semi emersed. rotala mexicana 'goias' stays small. so does staurgyne repens. then you have hc, glosso, pretty much ground cover, it really depends on what look you are going for.