15 Gal. "designer" tank

Hi All,
   I have a space in my office too small to put most tanks that will just fit
a "15 gal designer tank".(13.5"wide X 13.5"long X 22"tall)  I would like any 
suggestions for plants and fish for a weird shaped tank like this.  
   I have had just a single Amazon Sword in it before.  It out grew the tank 
quickly.  It shaded out any lowlying foreground plants long before was press-
ing against all 4 sides.
   I plan on redoing the hood to use two (4?) 9W, 5000k mini flourescents 
(Oshram?) I had previously supplemented the little 12" flourescent (6 or 8 
watt, I forget) by directing some incandescent light in from the sides.  The 
Amazon Sword did surprizingly well in this marginal lighting with diy yeast 
CO2 and a heavy fish load.
   The water here is fairly hard and pH 7.4 as it comes out of the tap, but 
of coures the pH is lowered by the CO2.
   I have considered terracing the tank in order to use fairly small plants 
in the back to avoid having just 1 large plant taking over the whole tank.
Tall plants that don't spread out much might be another solution for the back.
If all else fails I will just set it up as a one plant tank again.
                Eagerly awaiting your suggestions,