The very best vietnamese restaurant to be found in Kansas City is the Vietnam Cafe located @ the corner of 5th & Campbell across from Columbus Park. Everything I have eaten there is quite delicious.
+1 on Vietnam Cafe, esp. the vietnamese crepe, because they're generous with the seafood, unlike most places that fill it with mushrooms and/or bean sprouts. Any pho and noodle bowls are also particularly tasty. They even do good chicken pho...