Another tip, leave the stem plant bunches together. You can space bunches farther apart and still have optimal visual body.
In that tank of that size I'd do two separate interest areas, one in each back corner, then coming forward. To do this, you'll need to do a fairly dense concentration in each back corner, then thin slightly following the side walls towards the front, getting shorter towards the front as well.
From there, I'd get a large decoration or a tall peice of driftwood and I would put it close to the center, but if possible, branching out to each side. The plants will draw the eye from side to side, with the large/tall decor in the middle acting as a focal point. (sometimes you *can* put things in the middle, you just have to make sure there's movement to each side as well.) :)
Put some small things, like your crypts towards the front, possible both together on one side of the front ornament, one a little in front of the other, to further offset the center and add low-front interest. I'd also either lose the pots, or plant them way deeper into ther gravel, so they're almost hidden by the gravel.
You're also going to need a LOT more light, especially if you go with cabomda. (And I'm probably spelling that wrong...sorry!) You can get two additional clip on desk lights, and put high equiv wattage (like 60 to 100) compact fluorescent lights in them, leaving them on for 12 hours a day. This will ensure enough light for the camboda, and also make sure that it grows quickly.
Oh, and floaters! I love floaters. :) Just make sure you don't coat the surface of the tank with them if you have moderate to high light plants underneath, but I can usually sort of clump mine together into a couple of spots and they stay that way fairly well, so my underplants still get enough light. Their roots hang down to create interest, and the slight shading in spots that they provide really makes the tank seem more full than it is.
Red Root (Salvinia), frog bit, water lettuce (mind, this grows up from the surface and forms a true plant, not just leaves), duck weed (very tiny), greater duck week (fairly large), four leaf clover (this is actually sometimes planted as well and then grows upwards), and fairy moss (azolla), and I'm sure there are others as well. :)
- if you use anachris, only use plain flourish, nothing with carbon or iron as it will melt your anachris plant.
- your crpyts are going to need root tabs to really grow well
- sometimes your fish will provide enough fertz and you won't need to use any liquid fertilizers, just depends on your tank and your fish. :)
- check the classifieds here for plants, and go to places like www.aquariumplantcentral.com
for really good, high quality plants in big bunches. Also, the Foster and Smith website sells plants for good prices, haven't ordered from there though, so unsure about size. :)
- avoid ebay for plants. There are a lot of foreign sellers, and there seems to be frequent problems with customs and people NOT getting their plants, or getting them dead months later. :P
I hope that helps!! :D