One is as you head into Puerto Plata from Playa Dorada, go past the first Isla Gas, then take the very next left hand turn (corner where Dinora Sportwear used to be) just up the block on the right hand side is the biggest and probably the best.
Second - harder to give directions - do you know calle Los Domingues? Behind the beer plant near la Javilla. Go up this street and over the little bridge and till you see the new baseball field then turn right. Go two streets and turn left. You will see it immediately on the right hand side of the road. They are good but smaller, better prices as a general rule.
Third - I have to get directions for you but start with these two.