Truthfully, I wouldn't put a single plant in a grow-out tank. they get in the way of the necessary cleaning, and they hold food.
On the other hand, if you're planting for a show tank, swords and anubis work well. I have also seen banana plants and a few other slow growers. I'd stay away from the ferny-type fast growing plants. They have a tendancy to grow too big too fast and then "burn out" in warm discus-friendly water. I am sure that some of the wonderful people here will have other suggestions as well.
Cheers!