We had a great time at Hanauma Bay.
A natural bay that is a protected sanctuary.  It costs $1 for admission and $5 per car for parking.  It is closed on Tuesdays and they provide an informational session on what not to do, like stand on the reef and don't feed the fishes.  Yum enjoyed herself and I loved the $12 underwater camera as I played Cousteau for the day.