Red wendtii would be perfect, because they tend not to grow up so much as out.
Also, Rotala rotundifolia looks super nice in my 5g, and under high light the variety I have turns to a beautiful pinkish color... but it requires constant trimming. What I do is just let the tops grow to the surface, then I clip the top few inches off, pull out the roots, and plant the tops where the bottoms used to be. It's an ongoing cycle, though, that I'm sure I'll get tired of soon.
Also, Rotala rotundifolia looks super nice in my 5g, and under high light the variety I have turns to a beautiful pinkish color... but it requires constant trimming. What I do is just let the tops grow to the surface, then I clip the top few inches off, pull out the roots, and plant the tops where the bottoms used to be. It's an ongoing cycle, though, that I'm sure I'll get tired of soon.