The only Vietnamese dish many people know is pho, the rice noodle soup. However, Vietnam has much more to offer than this simple dish. Our favorite is actualy fried egg noodles, called mi xao. Also look for cao lao, a specialty of Hoi An, made with thick rice noodles topped with pork.
You can find good cheap food everywhere you go. There's no reason to starve on a trip to Vietnam!