Speckled Moray Eel
There are two different species of Moray Eels in Sydney - there's the Speckled Moray Eel which is yellow and the Green Moray Eel which is also yellow. Fortunately the Speckled Moray is actually speckled so it's easy to distinguish which is which.
Green Morays are the larger of the two and are very common but Speckled Morays are few and far between. The best place to see them is in the harbour.
The best thing about Moray Eels is the fact that they have two sets of jaws, but you'll have to read the Green Moray story for that one.