just got back from saigon. district one is where alot of the action and touristy areas are. must see or do, rooftop at sheraton or caravelle for drinks at sunset. ben thanh market to shop for all kinds of junk. street food is good and cheap. get used to the exchange rate about 20,000 dong to 1 dollar. it blew my mind pulling out 4 million dong for the first time. cu chi tunnels were decent. we took a biking trip up the mekong delta and that was decent, i wasnt super impressed with the delta. the war remnant museum is a joke(aka the war of american aggression but at 75 cents its worth the entry fee). if you do any tours pay a little more and get a good tour guide/company. it will be worth it. there are alot of parks and areas to run and work out, which was nice. pick up a lonely planet over there as well. street vendors in district one will be out at night and selling them for just a couple bucks(but youll have to negotiate to get it for 2 bucks which i love to do just keep it super friendly).
phu quoc island was really awesome, highly recommended. there is a good night market to eat at on phu quoc. also rent a scooter and cruise around the island.