Just found this board a few days ago - definitely my loss, it's a great board - and already have seen several taco stand or in search of burrito threads.
The search for great taco stands and burritos are noble causes all. I feel fortunate to live in Culver City and have El Abajeno, Taqueria Sanchez, Mi Ranchito, Titos and a number of other awesome and authentic places within a mile or two of my house.
My kids go to school in Santa Monica, so I'm also fortunate enough to be able to frequent the South Samo places like La Playita (seen a few mentions on this site already) and the Pico corridor, which includes restaurants like Gilbert's, Lares, Don Antonio and the great Oaxacan place El Texate.
I'm lucky, I know. My in-laws in Irvine eat at Rubios and pretend it's real.
But I have to throw La Super-Rica Taqueria into the discussions. It's in Santa Barbara, of course, so it's on no one's way home. But to those on a quest, I recommend putting it on your list of destinations. Much has been written about La Super-Rica Taqueria so I won't add much more. I'll just link a website and you can google search for reviews.