Taste of Mexico is tucked away in the Princeton Shopping Center. It could be mistaken for a very average restaurant, but inside, you'll find the most authentic Mexican food in NJ.
They boast the best burritos I've had outside of Mexico, and even the lunch-size is enough to feed the hungriest individual. What sets them apart is the marinated beef steak (bistec) that is used instead of the ground beef you'll find elsewhere. The beef tacos and burritos feature this on great soft flour tortillas that are always very fresh. Also try the variety of bistec dishes including Bistec a la Mexicana. The guacamole is amazing and always freshly made to order with onions and cilantro, assuming they have good avocados on hand. On request, the will add a little fresh jalapeno to the guac to give it a little extra flavor.
The owner, Felipe, is quite a character and wastes no time getting to know you if he's on hand that day. Outside seating is available on nice days. And the service is generally quite good.
You can BYOB from the liquor store in the Princeton Shopping Center, too.