Playa Manzaillo is southwards down the coast from Zihuatenejo. There is a live coral reef with diverse and plentiful fish populations. I reached it via a commercial sail tour, one can also rent a small boat from the harbor. The sail tour was the typical (fun) adventure of motoring over with an open bar (for after snorkeling, for me... thank you) and sailing back. When we re-entered Zihuatenejo bay the boat stopped for spinaker sailing where the spinaker sail is released and folks can climb in a harness and sail, sort of like stationary parasailing (alot of fun).
The commercial tour is a little pricey (USD 50), but fun with a hard working, very competant, and friendly crew. Lunch and cerveza were provided. My only real complaint is that the boat (Tristar) is big (65ft)... which is great if one is subject to motion sickness, but means there is lots of company on the boat.

 

 
above:
barely visible trumpetfish and a coral close-up

 

spinaker sailing (playa la ropa in the background)