The lady at Petco gave us some water wisteria plant clippings because we are in there so much and she didn't want to throw them away. This was roughly 6 weeks ago and they have grown so much, I now have a wisteria clipping in every tank in the house and the 46 gallon and 29 gallon have 4 fully grown huge stalks of it a piece, So beware that it will grow extremely fast and be easy to spread around if it is the same as what we have.
He is going to order us a few dwarf lily's for the 2 large tanks and I am so excited. They are absolutely beautiful.
I recommend water sprite also, if you wanted to vary from the wisteria. We have in one 10 gallon a large plant of sprite and it is easily the most beautiful plant we own right now. Elvis (king betta) hides and sleeps in it frequently.
I also highly recommend anacharis (the large, thick stalks) not the skinny little one - they grow across the water line and all the bettas sleep on them. We have so many plants, all the betta leafs we bought hardly get any use at all any more.
We also have an over abundance of a plant that came free with a few orders from Tricksters (no idea what it is called) but soon I am going to have to start selling bundles because it grows so fast. They are absolutely beautiful as well, especially for good size for normal bettas to sleep on.
Also if you are going to us any type of gravel or sand over the eco complete, I highly recommend a light color so that the light bounces off of it, darker colors make it harder with the dividers for the light to hit the plants as easily. (from my personal experience not everyone will agree with that.)