Floating plants tend to be the best at filtering, especially those that are surface floaters and have the aerial advantage. In particular, Duckweed, Salvinia, Frogbit, Water Hyacinth, and Water Lettuce to name a few. Among those I would suggest Salvinia and Frogbit as Water Hyacinth and Water Lettuce are more suited to ponds, and I don't recommend Duckweed any longer because it is such a pain.
Submersed floating plants like Hornwort and Anacharis tend to be regarded as good filterers as well.
The other type of plants that are considered good filtering plants are those stem plants that grow emergent, such as Ludwigia, Alternanthera Reinecke, and Pennywort to name a few.
Not sure if this helps, but stem plants utilize nutrients (mulm, detritus, etc.) from the substrate better than floating plants (more or less obvious, I know). I use a mixture of all of them to try to keep things balanced.
