Being a SoCal transplant, I have always been on the lookout for the best Mexican in Portland. I still have yet to find anything on the caliber of the taco stands in San Diego, but it is still pretty good:
Cha Cha Cha: Becoming the leader in town in cheap mex. $1.25 tacos in the Pearl? Are you kidding me? Great Carnitas and lots of options. Hard to go wrong. Wish they offered a fried (hard) taco shell, though I'm yet to find a place in town that does.
La Sirenita: Pretty authentic, but man the onions just kill me at this place. I still love it, and it is less than 1 mi. from where I live but with the lines I will often just go 1/2 block to:
La Bonita: Where I find the al pastor better than La Sirenita, but most items are a slight notch below.
Baja Fresh, Aztec Willie chain, etc, are too expensive to consider for this post.
I have tried others like Burrito King, and thought it was ok. Anyone been to just a total dive that turned out to have just amazing tacos/burritos?