Consider a trip to Qui Nhon as a less visited alternative to Nha Trang. For a bit of adventure, travel to Dong Ha in Quang Tri. There's not a great deal to do in town, but it is ideal for bus or moto day trips to Lao Bao. The mountain region and countryside near the Lao border is like another world.
Plane tickets are needed, but if your travel budget permits, look into some relaxation time on Phu Quoc Island.
If you're looking to escape the crowds, I would recommend heading to the Cao Bang area near the Chinese border. It's a bit of a hike, but well worth it -- the scenery is stunning as you head out of town and up into the mountains. Thac Ban Gioc is a waterfall about a 2 hr drive from Cao Bang, and it's really nice -- spans the Chinese-Vietnamese border.
Ba Be is also a nice little getaway that's a bit off the beaten path. It's probably going to be a bit more popular w/the other roadtrippers, but we had friends who were there last year and said it wasn't too bad during the holiday weekend.
Why dont you try Ninh Binh.
100km from Hanoi. you can go there by bus or motor-bike.
The place is nice and the price is good, better than Hanoi. A hotel room price ranges from 5$ to 15$ per night.
More about details:
It is a nice place with a lot of landmarks like Tamcoc-Bichdong (Tamcoc looks like a natural tunnel that go through 3 mountains, you can hire a boat an row in there watching the paradisal scenery, its pretty cool, Bich Dong is a small cave not very interesting, but from the plot you can have a pretty nice panorama of the place, its just like 'inland Halong Bay'), I really love it. Besides, there are PhatDiem Cathedral (a small stone-made cathedral), Baidinh Temple (considered by many as the biggest temple in South East Asia), VuaDinhVuaLe, Cuc Phuong Botanical garden (Biggest in Vietnam), ancient capital Hoa Lu, VanLong Landscape...
Feel free to ask me more if you need help.
Minh.