As far as Mexican food goes, I haven't really tried a tex-mex place in Buenos Aires, but I did go to an excellent Mexican restaurant a couple of times. It's called Frida Kahlo, and it's in Belgrano. They have some plates that are actually authentic Mexican, and if you ask for it, authentic Mexican salsa. They have some more toned down plates like tacos, which are close to the real authentic Mexican tacos. I know that's not Tex Mex, but the food was not back if you have a hankering for something spicy with very strong flavors.
For seafood, there are some good places expats might not know about. The first I would recommend is a pescaderia in Flores. This place is not a restaurant, but they have fairly fresh seafood. What's really nice is that you can order the fresh food, and have them cook it literally however you like in the moment. They'll put it in a box and you can take it with you. They also have pre-prepared stuff. It's quite reasonable. The place is over a couple of blocks from Plaza Flores, on the street behind the church. Just get off at the plaza and ask for the pescaderia, because I don't remember the name of the street it's on. The place is always full, of course.
Another place where you can catch good food/seafood, is Tia Margarita over in Caballito on Jose M. Moreno and Pedro Goyena. They have some good seafood plates, and the paella was pretty darn good. Actually, anything at this restaurant is unbelievable. The place is very pricey, but plates are massive, and you can probably share to help mitigate costs. Be prepared to wait if you go during a peak time, because it is freaking good. The menu had about 200 different plates on it for those of you who complain about variety.
The final place is a pescaderia on Pedro Goyena and Senillosa. It's not a nice looking place, but serves good seafood, and as a consequence is pretty much always full. You can sit down and order off the menu, or buy the fish and take it with you, or ask them to cook it and then take it with you.
For other ethnic foods, there are tons of Greek restaurants, but I recommend the Armenian neighborhood in Palermo. Take your pick, and you'll probably find a pretty nice Aremenian restaurant with great food (it's basically Greek food).
I miss good Chinese food. I read the other day they are building a PF Changs in San Isidro. Thank goodness. A Pei Wei would also be welcome.
People complain a lot about the food on this website, but frankly, I don't get it. Unless you have a serious hunger for spicy food, I think the food in BA is pretty great, although there is not all the variety there is where I come from.
