Thanks Cheri! Yeah I was planning on using a live moss like Selaginella uncinata, but I actually think I like the look of the sheet moss a little more. I'm hoping that between the crypts and the moss that I won't have too much of an issue with soil getting into the water.

I've decided on a couple plants that I want to use, they are:
Crypt Parva (in the gravel next to the "creek")
Green Mondo Grass (the very back coming out of the water)
Duckweed (not sure on it yet, but it would cover the surface of the water)
Crypt Wendtii (possibility, I've only grow it submerged so I don't know how tall it will get out of water)

But I'm still not sure on what kind of plant I want in the back corner, or what to have growing out of the water and randomly on the land part.
Any suggestions on a plant that will only have a diameter of 3 or 4 inches and won't grow over 12 inches tall (or can easily be kept trimmed down)? Or a plant that will only grow about 4 inches tall?