Places to put on your list:
Damajagua (Imbert, Puerto Plata -- walk up the hill to slide down the 27 falls -- guide can be booked at the Damajagua guides at the side of the road -- go early). Puerto Plata has plenty small low cost hotels.
Samana (lots of low cost hotels). El Limon Cascade. Playa Cozon and Playa Bonita. Also Portillo beach is good for kiting. Playa Rincon. Take the ferry to cross over to Sabana de la Mar.
Caño Hondo hotel in Sabana de la Mar. Los Haitises. Miches and visit Playa Esmeralda (near La Mina).
Macao beach. Bavaro, Cortecito and Cabeza de Toro beaches. Take the Sitrabapu commuter buses.
Boca de Yuma town. Take the boat trip up the river, visit the La Playita across from the river mouth, and visit the Ponce de Leon house in San Rafael de Yuma.
Bayahibe. Book a snorkeling tour to Catalinita island with a stopover on one of the beaches of Saona Island. Dominicus beach (between Iberostar and Viva Palace).
La Romana. Altos de Chavon.
Santo Domingo (colonial city).
Constanza. Stay at one of the small hotels and book an excursion to Aguas Blancas falls.
Jarabacoa. River rafting with the Rancho Baiguate people.
Santiago. Centro Leon for insights into Dominican culture.
Puerto Plata -- visit to the Victorian city and the Isabel de Torres botanical garden (skylift trip).
Last day on Sosua beach, right next to the Puerto Plata airport.
For more information on these spots, see
http://www.dr1.com/travel
Some hotel recommendations at
http://dr1.com/directories/index.shtml#Hotels_Resorts