this place has plants by region they are found i dont know what it has for floating plants but it should give you an idea of other plants you could put in it.
Get frogbit . I gave lot's (had to much growing in pond) to my brother in law he has a 55 gallon with 3 -40 watt Daylight bulbs and it's growing great.
Leaves are smaller but growing great .
The drawback is it doesnt like current and leaves can't be submerged and they do need 1 to 2 inches of space as they will grow up that much other than that nice looking and fish love the large root's it sends down .