I think your choice might be wider than Thomas suggests - I've got Glossostigma elatinoides (available from the above links) growing well in a tank with approx 2WPG over it. The tanks 18x15x15", 60 litres or 15 US gallons, lighting is an arcadia luminaire with two 14w (15") tubes, total 28W:15gallons. The tanks 15" tall, and the luminaire means the lamps are another few inches above the tank. The Glossostigma grows via underground runners, and only produces leaves flush with the substrate, which is supposed to be an indication that it is not light starved. However, the tank is dosed daily with TPN+, and has a timed pressurised CO2 system, so you might have a harder time than I do. Also, I don't know how tall your tank is, or what the lighting setup is - I always find it easier to visualise tanks if I'm given dimensions rather than volume.
If your tubes are movable and you choose a light loving plant for the foreground, and less demanding plants at the back you could look at moving at least one of the tubes to be right over your foreground. And if you've got a hood and you think your foreground needs more light, you could just add additional lamps.
I love all the plants suggested so far (C parva, Eleocharis, Glossostigma) and have them all growing in amongst each other in my tank.
Others to try could be Pogostemon helferi (doesn't seem to be too demanding at all, but might need replanting every few months if the old leaves start to look scruffy), many other small varieties of Cryptocoryne, or what about small stones/wood with low plants attached - mosses, Anubias, Riccia (light loving and high maintenance).
Basically, the Riccia is extremely high maintenance, and quite demanding when grown submerged (highest maintenance), the Glossostigma and possibly the Eleocharis will need fairly regular trimming (medium maintenance), mosses might need the occasional trim depending on how fast they grow (probably not too fast with low CO2), Anubius will need almost nothing doing to them (perhaps remove very old and ugly leaves)(low maintenance) and Cryptocorynes will need only the most occasional maintenance (take off any very old leaves). In fact, the less you do to the Crypts the better, especially for the first few months - resist the temptation to do anything to them, or move them, and suddenly they'll take off.
Look at pictures on the web and see what you like, decide how much effort you want to have to put in to keep the tank looking good, and just try things. If you start with a small bit of a plant and it doesn't do well in your tank you haven't made too much of an investment. If it does take off, and you like it, you can either buy more, or spread the new growth over the area you want. Don't forget that if it doubles in (eg) 3 weeks, then you will have four times as much as you started with in 6 weeks, and 8 times after 12 weeks!
All the best with this tank!
Mark
PS - if its 48x18x18" it's one of my favourite tank sizes! Deep enough (front to back) to create a good effect, and not too tall to reach the bottom. It should look great!
