At Nusa Lembongan ans Nusa Penida you can encounter the rare and spectacular Sunfish or Mola Mola.
At the Gili Islands you are almost guaranteed to swim with seaturtles when diving or snorkelling.
These are just three of Bali's many great dive destinations. To give you an overview of all of them we have written a e-book, where you can read about all Bali major dive destinations. It's free of course and you can find it and download it here: Diving e-book