Agree with having a guide. We were lucky enough to stay with a Vietnamese friends family who still have a house there somewhere between Saigon and Me Tho. We basically ended up going with them on their family vacation. I'm still not sure where some of the places we ended up were but we were the only Honkies almost everywhere we ended up.
We did a Mekong River tour out of Me Tho. Spent some time at Grandma's place somewhere around Go Cong close to the coast, and hung out in Can Tho. Took day trips to some beach that I still am not sure of the location, and Nui Ba Den (Black Lady Mountain) that is big with the locals.
On one of our day trips to Saigon we hit:
Bing Tay Market-Huge indoor/outdoor market est. 1826
Reunification Pace-Very cool. Beautiful grounds and you can stroll through the whole palace on your own. In the basement the even had a shooting range and still had combat engagement maps from the war.
General Post Office
Notre Dame Cathedral
Finish up as the sun sets having a Martini on the rooftop bar at The Rex Hotel, where they had the daily press briefings during the war. Lots of heavy hitters used to get drunk there.