I was hesitant to put this in the LA thread...but I know how obsessive many of the 'hounds are. (i.e. willing to drive hours for the goods)
Go to Isla Vista, the college "town" north of Santa Barbara. There resides a place called Freebirds. It's open 24 hours. My previous memory of the place is pretty blurry, (don't ask how drunk I was) so I finally visited the place again with 3 friends, months later. Closer to what people imagine a SF burrito to be. Lots of choices. Whole/refritos, types of salsa, lettuce, etc. Choice of veg, grilled chicken, or asada. The grilled meat is just so fantastic. I'm a Meat/beans/rice type of guy at heart, but the grilled meat at Freebirds is just so flavorful and the toppings well prepared that I'm becoming a fan of the "picnic basket" burritos. Monster burrito is just over 5 bucks, and it's big. Well worth it. Next time I go I'm buying 10 and freezing the leftovers.
I'll edit this to add info on how to get there...I would honestly skip out on that pilgrimage to La Super Rica (Yes I've been there many times) and drive an extra 10 minutes to Freebirds.
Too many bros and slutty chicks in the area for my taste, so my friends and I found a park about a block away with a bunch of crazy drunk homeless people yelling, that's our crowd.
ETA:Freebirds World Burrito
879 Embarcadero Del Norte - Isla Vista
Phone: (805) 968-0123
P.S. shoot, I also found a Santa Barbara site with tons of horrible reviews for the place...maybe inconsistent? I dunno, I've eaten more mexican food than I can remember, everything from authentic, to SF, to gringo, and I still thought Freebirds was pretty fantastic. Try it if in the area...