If you're in Ho Chi Minh area, a town called Mui Ne is not that far north along the coast, and, at least back in 2003, found it to be a really worthwhile chilled out beach town. At that time, it wasn't too crowded either. Careful if you're there around TeT though. The locals are friendly to the point where, a brief conversation leads to shirt trading and drink quaffing, and the potential exists for your Honda Dream (scooter) ride back to your hut to turn into disaster (or an impossibility).
http://en.wikipedia.org/wiki/Mui_Ne