Part 1 of a long update on things in Vietnam outside of Saigon. I think I mentioned before that I spent about a month there four years ago (with a side trip to Siem Reap).
1). Hanoi- Love love love Hanoi. I preferred it to Saigon- slightly cleaner, cooler temperature, and generally less overwhelming than Saigon. (Having said that, I think you're going to India before Vietnam, and nothing will be more overwhelming than India from what I've heard!). I spent 3-4 days there, and if I return to Vietnam I will definitely go back to Hanoi. While you're there you must: go see Uncle Ho's embalmed body (how can you not?); check out some of the temples, gardens, and architecture, find cafes for vietnamese coffee and coconut ice cream, see the Water puppets show (touristy but cool), and shop for cool trinkets (esp. embroidered linens, chopsticks, etc.).
2). Ha Long Bay- This was the highlight of my trip to Vietnam. If you can stay longer than 2 days do it! (If I go back to Vietnam I want to go kayaking here.) It is easy to make arrangements for Ha Long Bay from Hanoi. We stayed in a boat in the bay overnight- it was comfortable enough for us. Gorgeous scenes with the limestone cliffs.
3). Hoi An- We flew from Hanoi to Danang and then took a taxi to Hoi An. (Didn't get to see Hue on this trip alas. I ended up staying in Hoi An for four days, as we just couldn't get our butts in gear to leave. We got suckered in to having lots of clothes made- including cute shoes and purses Chrissy! Don't get too suckered into that, instead enjoy a peaceful, little town (the most mellow you'll probably hit in Vietnam.) You must try Bier Larue (the beer of this part of Vietnam)- it is my favorite Vietnamese beer. We also took side trips to the Marble Mountains for hiking (OK) and to the Cham ruins at My Son.