Brief note: have tried both Lee's Sandwiches (which came down from my hometown, San Jose) and Banh Mi Che Cali. While Che Cali is my favorite che joint in all of Little Saigon, I dislike the sandwiches. Find their meats subpar. Lee's has also lost something in the tranlation from San Jo. Both use kinda crappy meats.
Have found one satisfying banh mi so far in town: Buu Dien (translation: post office), in the strip mall across from Pho Hoa in Chinatown. Had the nem nuong (sweetened pork ball). Solid, non-greasy, flavorful nem nuong with good condiments.
Not as good as the best in San Jo, but a very satisfying banh mi.
Banh mi take home tips: I do this all the time, partially due to the extraordinary cheapness of banh mi. Refridgerate your sandwich. It even freezes well. (If you freeze, take the pickles out and keep them in a jar). To reheat: defrost the whole thing first if frozen. Then, take to pieces. Microwave up the meats, toast the bread in a toaster oven, leave the pickles in the fridge til the last minute, so they're cold. Reassemble.