We like beaches, parties, and meeting people. No budget at all.
We were in Vietnam for two weeks and traveled from Hanoi to Ho Chi Minh. Our itinerary was:
-Hoi An one of our favorite stops in Vietnam, you can ride your bicycle to the beach too.
- we stopped quickly in Nha Trang, along the coast where there are beaches.
-Mui Ne for the sand dunes and beaches
- Ho Chi Minh City with an overnight in Can Tho to visit the floating markets at dawn.
Some people we met recommended Sa Pa, northern Vietnam for great scenery and cooler climate.
I've written all about our trip with pictures and travel tips here: http://www.ooaworld.com/category/vietnam
Mentioned in this answer:
These are happening places with a young crowd.