New Orleans has incredibly good vietnamese food. I've added my two favorite places - Dong Phuong in New Orleans East (in the vietnamese suburb of Village de L'est), about 11 miles NE of the french quarter. Incredible, cheap, and so out of the way that only locals ever go there. Restaurant only open for lunch.

I've also added my go-to when I don't feel like driving way out to the east-- Tan Dinh, across the river in Gretna (about 6 miles south of the FQ). Other well known places in the area are Nine Roses and Pho Tau Bay (which is good but I think is overpriced).