Does anyone have any other favourite floating plants?
My favorite floater is frogbit (Limnobium laevigatum). It's large enough to be easy to scoop out of the tank, grows quickly, has thick leaves that can withstand some current (it's good at resisting being tossed under by the current), and I like the look of the long roots floating around.
I also like red-root floater (Phyllanthus fluitans) because it has such a great color, is also large enough to be managed easily, and grows quickly when it's happy. It is more delicate than the frogbit and can get knocked around by the current. It doesn't do well for me when I use a glass cover over the tank unless there's a good deal of air space and air circulation.
I also have Salvinia minima and it is a decent floater. It multiplies very quickly and is many times larger than duckweed so it is easier to manage, though not as easy as the frogbit or red-root. It tends to need decent airflow and is easily knocked under water by the current since it has a much a smaller size than the frogbit or red-root.
I've managed to get rid of duckweed out of all my tanks except one. I find it to be a true nuisance and I became very tired of having green bits stuck on my arms after any tank maintenance even after rinsing them off (BTW I'm female and not particularly hairy). It's such a pain trying to scoop out the excess since I had to net it and then it stuck to the net (and my hands, and the bucket, and anything else it comes into contact with).
I never had much luck with water lettuce. I had it for 6 months or so and it grew well and then it gradually dwindled and died off, I'm not sure why. After it failed I tried the frogbit, red-root floater, and Salvinia and they've been growing well for me for years now. I regularly dump handfuls of them in my compost pile.
Oh, I also have Ceratopteris pteroides which can get very large (12+ inches across and 6 inches above the water surface with roots that can get over 6 inches long and form a mass about 4 inches in diameter). It takes a while (think in terms of months) to grow that large but is only suitable for larger tanks. It doesn't seem to grow particularly fast unless it has a lot of light. And it's VERY good at blocking light to the rest of the tank.