I'm no expert, but really it is mosses, Monoselenium, Microsorium, Bolbitis or Anubias. If you are injecting CO2 then Riccia can be grown attached to things.
Monoselenium is really easy and prolific, covers a multitude of sins etc. Microsorium is easy. I've just acqiured a bit of Bolbitis, so we will see how that does.
The various forms of Anubias grow attached to things like rock or wood. Anubias nana 'petite' should be available in your nearest Pets at Home or fish shop. The other species are mostly mail order and are fairly expensive, more than a tenner per plant say.
Does this help ?
Cheers
David