What plants are good for humidifying the air?

Me and my brother each have asthma, and one thing that compounds any breathing difficulties is arid air. I remember researching plants some time back for their air filtration effects (we bought a hepa filter in the end), and saw that some plants serve a role as humidifiers as well. What plants are good at fulfilling that role and also are simple to take care of, not poisonous to cats, and don't take up enormous amounts of space?