It all depends on what resort are you staying. Near Fiesta/Flamenco/Paradisus is Plaza Bavaro. During the day it's mostly a tourist market, many shops that sells all type of souvenirs.
At night, it's a place where many of the employees of the resorts go to hang out (I don't know if this expression is correct). I think there are at least two little restaurants, some bars (two in the middle of the Plaza) and two discos, Coco's (I didn't try it, but I think it has more tourists than locals) and EL RINCON, a little disco that only plays Bachata and Merengue and which is really full of locals (it's the best place to dance "real" merengue).
I've heard about some places near Melia Tropical/Caribe, but I haven't proved them.
Hope to have helped you. And, of course, don't forget to try Captain Cook at the beach, beside Fiesta Resort. It's a bar-restaurant-supermarket quite nice... (and you can go there free by boat...)
