Just returned from Vietnam and used myvietnamvisa.com to get a visa on arrival. It was quick, easy, and I had no problems when entering at SGN. It's legit; the New York Times even had an article on it.
AA ACs: All US hubs; BOS; SFO; NRT; SCL; EZE. FLs: LAX; MIA. BA F (SFO, YVR, LHR). CX F, J (HKG). JL F (NRT, HND). LA J (SCL). IB J (MAD). JL J (TPE)