I was in Reading last weekend to see the contemporary Mexican art show that's now at various venues in and around the city. Was looking for a suitable lunch and stumbled on a great taqueria, selling out of a trailer, with outdoor tables under a canopy. It's on 6th street, heading away from downtown, on the right, just before a railroad overpass. Sorry but I didn't remember to note the name or the exact address. It's related to the Mexican grocery next door (a rather good one).
There was a limited menu: 4 kinds of tacos: adobada (pork), bistek (beef), asada (grilled steak), and lengua (tongue), $1.50 each. We had the pork and the grilled steak. They were excellent, on double tortillas, served with chopped onions and cilantro, and lime. There were two good table salsas, one green and one red. They also had tostadas with ceviche; these were excellent too. The only other thing served were "elotes exquisitos"--corn on the cob, slathered with mayonnaise and rolled in grated cheese, with chile and lime--they looked just like the ones I've seen sold on the street in Mexico, but I didn't try them. Drinks--all the usual juices and sodas--were available at the grocery next door.
Well worth a stop if you're in the area. I'm not sure of their hours or days of operation, but I saw a sign saying, if I remember right, that they serve the elotes only Thurs-Sun.