This is a branch off from the earlier topic on upscale Mexican (http://www.chowhound.com/topics/show/...). As several have pointed out, there is no truly great upscale Mexican food in the Boston area. For my money, the best Mexican food to be had in Boston is at tacqueias, most of which are a good sight cheaper than Tacos el Charro in JP (see 'upscale Mex' posts on that topic). This is the usual response when someone posts asking for Mexican recommendations, so it makes sense to start a dedicated thread on the matter.
Tacos Lupita (which is actually Salvadorean, but the cuisine is similar) is far and away the winner here, and there are several other posts to this effect on the boards.
Boca Grande is cheap and solid if not excellent. I recommend pozole, black bean soup and the pollo al carbon. Their enchiladas are weak.
Tacqueria la Mexicana in Union Square is inconsistent. Several times I have had what my former roommate dubbed 'tuna salad style chicken' tacos, which is disturbing. Other times I have had great food there. The Aguas Frescas are consistently good.
These are generally the places I frequent. I have heard good things about El Pelon's fish tacos (what about their other stuff) and mean to try them. Other than that, any other contenders worthy of mention?