I also love water willow. It's easy to transplant. The nice thing about it is that it will only grow in shallow water. If it takes up too much space for your liking, it reponds well to chemicals, but it is very easy to manually remove.
Blue flag iris is also a nice shallow growing plant. I've even used a plant called sweet flag. It looks like a cattail, but it doesn't grow very tall. In fact, you can cast over it. This particualr plant smells like juicy-fuit gum if you snap the stem and smell it. If you lick it, then you'll go on a mind trip that would make Jim Morrison proud. I'm just kidding. I've never licked it, and I have no idea if it will alter your mind.
