When I was looking to improve my aquascaping I went and looked at the entries for the AGA Auquascaping contest.
http://showcase.aquatic-gardeners.org/2005.cgi
The nice thing there, is you can see pics of the tanks. The entries have a layout and list all the plants. Plus, these are judged by some well known Auqascapers, Amano etc. You can read thier comments about every tank.
In my case, I picked up on the idea of spliting your tank into 5 sections to lay things out. At 48" long, i put a piece of tape every 9 1/2" along the front to give me a guide. The left 2/5 of the tankmake one foreground area, which is surrounded by taller plants. Then at that second mark from the left I put in the Driftwood (at an angle in zen garden style). The right 3/5 of the tank makes up the other foreground zone, which is also surrounded by tall plants.
As for your tank, first off those plants look great. I bet it is so cool to see those Angel fish cruising through the swords. I think that if you broke your tank up into 1/3's you can make some nice zones. It looks like maybe microsword along the front, that looks great, leave that. On the right side 1/3 you could get a nice piece of driftwood, or some rocks. If driftwood, you could lay it so the bottom is in front at that 1/3 mark, and the other end was in the top right corner. Then plant the I think it's water sprite in front and around the driftwood, and it looks like one other stem plant on the right corner (Cabomba?). That perhaps can make up the background there.
In the left 1/3 perhaps create a nice effect with those swords. Take the smallest one and put it in the front left corner. Then plant the 2 next larger ones behind that. Then 3 behind that etc. It looks like at least 6 swords there. The last row should be along the back and go to the 1/3 mark.
That leaves the center, You could put the tall grass (Val? Sag?) all allong the back in tne center 1/3. With the Pennywort in front of it. The penwort could overlap into the left 1/3 some too.
Anyways, thats what came to mind looking at your pics above
Those swords will easily hit the surface in that tank I think. Which should look real nice and fill things in more. The pennywort can be kept under control by snipping the growing tips and keeping light on the lower leaves.