When someone mentions Bali, Nusa Penida and Nusa Lembongan are the first to come to mind, followed by Menjangan Island (in the north). But if you're into macro diving, Amed and Tulamben offer some good muck diving. The Liberty wreck in Tulamben is a not-to-miss dive spot - the wreck is beautiful and large! But apart from little critters, Manta Point is the place to visit. Adventure Divers, the dive company I was with, do day trips towards the south to dive with Manta Rays. Its almost certain you'll see one if not a few Manta's at this dive site in Bali (and its all year round!).