Spent 4 days in Saigon in May, awesome time, loved every minute of it. Some highlights for me:
Cu Chi Tunnels: This is a really cool thing to see, especially from an American perspective. The videos they show you are propaganda films from the government about how the Americans descended on a peaceful farming village "like a pack of crazy devils". I don't know how you would arrange it, but our tour guide was a guy named Mr. Binh, and he is a Vietnamese guy from Saigon who fought for the US side, he spent 7 years in a re-education camp after the war. He really gave some great perspective.
Look up Zoom Cafe, it's located close to the backpacker district. It's kind of expensive compared to other tours, and it sounds cheesy, but it is an awesome time. They put you on the back of a scooter with a guide, and a couple of hostesses take you around the city to different restaurants and bars and stuff. Tons of fun, owned by a guy from South Carolina.
The "Reunification Palace" is another place worth a quick visit, again for the contrast between the official government version of what happened and the American US History Class version.
We took a quick trip down the beach at Mui Ne, which was nice. It's a lot like Mexico, actually, and the seafood is damn good.
Feel free to PM if you have specific questions. I also visited Bangkok while on the same trip and have some suggestions if you need them.