Head on back to Iguana Reef resort and get a few drinks at the bar. About 30 yards off the shore, you'll see 2 bouys... there's an artificial reef there (wrecked boats, bikes, some big plastic thing, etc.) where tons of beautiful angelfish hang out. We saw some jellyfish and some sea stars back there too; and my personal favorite, those tiny little purple fish with the yellow stripes. Go on a clear day though, and watch your fins- the sand gets kicked up easily and clouds the water.
Enjoy!!