@mazda6,
I have a travel blog on Vietnam with pictures of many of the most interesting sites in Vietnam. In addition to HaLong Bay, I would highly recommend HoiAn, Nha Trang, and Saigon and Hanoi. The reason I'm recommending these two major cities are 1) many good restaurants, 2) interesting sites, and 3) you can really get the flavor of Vietnam. If you need some recommendations on restaurants, just let me know. One of my favorites in Saigon is the Mandarin. The service and food there are tops.
My travelogues are at,
www.travelpod.com/member/c.i.222 I've broken down my travelogue on Vietnam by cities. Start with "Covered most of Vietnam" in Hanoi.