Duckweed: Duckweed are little green plants that float on the surface of the water. They resemble tiny little lily pads. They consist of two leaves with roots on the bottom that eventually grow more leaves and divide to make more little duckweed plants. I think they look really cool as they float freely across the surface of the water. These little plants reproduce very rapidly. You may need to eventually remove some and toss them out because they can quickly cover the entire surface of your aquarium.
Pothos: Pothos are a broad leafed green plant. Pothos can be purchased for a relatively cheap price at any home and garden store. Although not naturally aquatic, I have found that these plants take to the water very well. They are very hardy and adapt well to most environments. I love them because they look nice and aren't too expensive.
Here is a potted Pothos I recently bought at a local home and garden store.
Here is some Pothos that I planted in my Aquarium.
