I visited Vietnam in late November through msot of December, and can tell you that there is a whole lot to see there. It's hard to find a place to start, so let me pick the top.
Ha Long Bay
This was the most incredible place I have ever seen on earth. Thousand of rock islands stretching as far as the eye can see. A six hour boat trip will take you through some incredible scenery. If you stay at Cat Ba Island, you will enjoy a very new and modern resort town. However, don't expect a lot of night clubbing. I think the bars close up by midnight.
Hanoi
Lots of incredible things to see depicting a culture dating thousand of years back. Hoang Kiem Lake is the center of Hanoi and is a beautiful place to take a walk and see the sites.
Hue
The ancient capital of Vietnam has some incredible temples and sites to see. Take a boat ride at night and watch the gorgeous singeres singing Vietnamese folk songs.
Da Nang
It's no longer a military base. It's a popular resort city that rivals any of the populat beach locations aroudn the world.
Saigon
What you may see in Good Morning Vietnam was over 30 years ago. Saigon looks more like Orange County, California. Big new high rises, lots of shops and reataurants. It is lit up like Las Vegas too.
If you're looking to get off the beaten path in Vietnam. That's real easy. a short distance from any of the major cities will haev you end up in a jungle, rice fiend or the ocean.
Good luck!