My all-time favorite is Playa Rincon, a few kilometers before Las Galeras. The road is a bit difficult, but the view of the beach is impressive.
Don't be afraid to go all the way to the right of the beach, the water is more quiet and turquoise there.
The "Playita beach" (ask for it in Las Galeras as it is tricky to find) is also wonderful and the water is shallow. That's your best bet in Samana
