Plants for guppy and neon tetra tanks?

I have two different tank I am setting up. One will be a 20 gallon guppy tank and one will be a 55 gallon neon tetra tank. What are some plants that I can get at a store like petco(only fish place around me). I wondered what are some low maintenance, no CO2 dependant plants that I could just drop in the tank where I want them and they would start to form their root system without much care.