Echinodorus bleheri
Amazon Sword Plant
Easy to find and a great and easy to grow plant. It's my understanding that the plant sold under Amazon Sword plant is most often an E. bleheri. This plant will live in almost any fresh water aquarium, often where other plants have been difficult to get going. It's a very hardy and adaptable plant.
Be warned though this get very large and will eventually rob light from the lower level plants. These really grow best in 20 gallon tanks or over. After about a year in a 10 it will have to be transplanted to a larger tank. These plants are really tough and can withstand some of the plant eating fish. I've had a large 6 year old plant cover a third of a 50 gallon fish tank and had 13 baby plants after blooming.