Triton is the largest moon of Neptune. Discovered in 1846, only 2 weeks after Neptune's discovery, it ranks as the 7th largest moon in our Solar System.

It is unusual because it is the only moon in the entire solar system that orbits in retrograde motion, i.e. the opposite way to the planet's rotation, leading scientists to believe that it was a captured Kuiper Belt Object rather than a body formed in the vicinity of Neptune.

Its orbit is gradually decaying so that in a few million years it will have moved so close to Neptune that tidal forces will start to break Triton up and we will have another planet that, like Saturn, has a marvellous and spectacular ring system.

Titan is Saturn's largest moon.

Nereid is another of Neptune's moons but very small by comparison.

Miranda is a small moon of Uranus.

More Info: en.wikipedia.org