"Two Step" at Honaunau (City of Refuge)
The beach itself is not remarkable and it's a little tricky getting into the water (despite its nickname "2 Step", but once you are in - it is amazing! If you are not an experienced snorkeler - please don't go in on a rough day!
Secret Tip: Parking can be crowded so, you may consider parking along the road. Also on the City of Refuge side there is a boat ramp that makes getting in the water much easier.
Take time to visit Pu'uhonua O Hōnaunau National Historical Park while you are there.
We were there for the last Annual Cultural Festival and even thought we had been there a dozen times before we were in complete awe. The Hawaii Pacific Parks does an amazing job of cultural research, education and maintenance.