Already got one
An anacharis(6-8 stems). I don't yet want to get anymore until I can successfully keep this one alive/well for a while.
Not to mention I change out decor every month. I don't want to root the plant if I am going to be changing stuff around so much.
Get the little "betta plants" that are a few inches tall. There .99 cents. Get alot. Get a terra cotta pot. Fill it with gravel/sand. Put all the plants in the pot. You can get a tall plant and put it in the middle. It looks really cool.