I just read about this, so I think that I can help. By the way, "Plants for Your Aquarium," by Wolfgang Gula, is the reference which I am using, and it is a good, cheap book on plants if you ever feel the need to purchase one.
Here are the suggestions:
Lake (Marimo) Ball--
Cladophora aegagropila. This is an algae, which is not often available in the States, but serves as a really good nutrient sucker. I'm not sure if the Marimo Ball is a floating plant or not based on my reference.
The classic Java Fern--
Microsorium pteropus. Pretty much easy to grow, and you could tie it to rocks if you want a rooted plant in your aquarium.
Water Lettuce--
Pistia stratiotes. This is a heavy feeder, but, for some odd reason, it says that they tend not to fare well in aquaria.
Crystalwort--
Riccia fluitans. Needs a lot of light, but, if given that, will spread like crazy.
Also, think about Duckweed (
Lemna minor), which is, oddly enough, not in my book, but seems to be very well-recommended in many of my fish-specific sources.
HTH (hope this helps, not hole in the head...I'd never wish that on anyone or their fish
),
Matthew