it depends on how much light you have, whether you're going to be adding fertilisers etc.
What sort of plants do you like?
Hemianthus micranthemoides would make a nice background stem plant. Grows to about 15cm but benefits from plenty of light. You could considers anubias nana if you're short on light. Mosses always look good
Hydrocotyle sibthorpioides (maritima) is quite pretty and stays small.
Glossostigma elatinoides makes a nice carpet.
Micranthemum umbrosum is quite a nice short stem, similar to HM. I have some of this in my new re-scape
Pogostemon helferi is something a little different in shape...
Echinodorus Tenellus (pygmy chain sword) is a nice small plant that looks great in a large bush/group
Echinodorus Latifolius (dwarf chain sword) is a slightly taller yet still small sword. See this pic for some of the above plants:
On the left side, the smallest plants ae E Tenellus, with E Latifolius behind. Theres about 25 of each plant in that section.
The short stem plant just to the right is Micranthemum umbrosum.
Just to the right of that, under the wood, is Hydrocotyle sibthorpioides.
To give an idea of scale, the tank is 1m long, and the Echinodorus group is about 15 - 20cm wide.
