Well best of luck with that! Choosing plants is a pain-staking process for me too, as I am also still learning. The good thing is, though, that they put lighting requirements and common names under each listing. As far as low-lying grass is concerned, they have a whole bunch of BEAUTIFUL dwarf sagitarria there. I just bought a handful of it yesterday myself. It's only $0.84 per plug, which at MW is like 1.99 per plug! Not only that, but at MW the sagitarria is all tall, and stretching for light, but the sag I got yesterday was grown submerged, under natural, full sunlight, so it's just short and healthy! And he didn't even count, he just grabbed a wad of it and said "That looks like ten plugs to me!" When I got home and separated it all, it was like 27 plugs!
It's when you are buying LOTS of stuff that this place would come in handy. I agree for just a bunch, or a pot or two, MW is more convenient.