There are many floating plants which are reasonably easy to grow. Depending on your tank you may need to add some nutrients - make sure you look for fertilisers that don't contain Nitrates or Phosphates as these encourage algae. I personally use JBL Ferropol but there is a lot of choice. You need to have reasonably good lighting for about 10-12 hours per day.
Some plants to look at (all info from www.tropica.com)
Riccia fluitans - Light requirements: low-very high, Hardness tolerance: very soft-hard, pH tolerance: 5-8, Growth: medium, Demands: easy. This plant can also be secured to rocks or wood underwater and will grow towards the surface. As a traditional floating plant offers good protection for young fish.
Ceratopteris cornuta - Light requirements: medium-very high, Hardness tolerance: soft-hard, pH tolerance: 5-8.5, Growth: fast, Demands: easy. Ceratopteris cornuta is suitable as a floating or underwater plant. If a leaf is allowed to float on the surface, small plants form on the leaf margin and can be planted in the bottom. In good light C. cornuta grows fast and helps prevent algae by consuming large amounts of nutrients. This makes it a good starter plant in large aquariums. The roots of the floating plant provide good protection for young fish.
Salvinia natans - Light requirements: high-very high, Hardness tolerance: soft-hard, pH tolerance: 5.5-9, Growth: medium, Demands: medium. Salvinia natans is a floating fern that grows quickly if there is sufficient nutrition and light. Light leaves are a sign of a shortage of micro-nutrients. Thin the plant to stop it taking light from the plants at the bottom. Salvina varieties have small hairs on their leaves, making them water resistant. Helps prevent algae by shading parts of the aquarium and using nutrients in the water.
Hydrocotyle leucocephala - Light requirements: low-very high, Hardness tolerance: very soft-very hard, pH tolerance: 5-9, Growth: fast, Demands: easy. A plant that grows fast and adapts easily, thriving in relatively hard water. Immediately after planting Hydrocotyle leucocephala will grow towards the light and the surface, where it will spread. It does not need to be rooted, but can be used as a floating plant which provides a hiding-place for young fish. (I personally have this as a floating plant in all my tanks - it grows fast and adapts well to most conditions).
HTH, Eddie
