There are several good travel guides on Vietnam, my preference is for Rough Guides.  Also useful is The Guide, published each month by the Vietnam Economic Times in cooperation with the Vietnam National Administration of Tourism.  It's available for $1 from news stands and is usually found in the rooms of up-scale hotels.  Vietnam Pathfinder is another monthly publication.  Its available for free from Vietnam Airlines offices and on their flights.  The Hanoi International Women's Club also publishes a book on moving to and living in Hanoi.

Below are some web sites that I have found useful.

VIETNAM EMBASSY IN WASHINGTON, D.C.
Provides visa forms that can be downloaded and printed.

JAN DODD'S VIETNAM PAGE
The web site, with forum, from the author of Rough Guide: Vietnam

VIETNAM ADVENTURE
Travel site for Vietnam with feature articles that change monthly.

EXOTISSIMO TRAVEL
Travel agency in Hanoi that specializes in custom trips for expatriates.  Great service, fair prices.

EASIA TRAVEL
Another good travel agency in Hanoi that runs a great sea kayaking trip to Halong Bay, among other trips. 

HUONG HAI JUNK
Luxury junk with nice cabins that cruises Halong Bay.  Better option for seeing Halong Bay in style than staying in a hotel and then cruising for a few hours.  Great seafood and lots of it.