I work at a mexican food restaurant, so I don't go out for mexican much, but if you want spicy, there are numerous thai places around the valery that always satisfy my hot tongue when I am in the mood for spicy
Tia Rosa on McKellips between Lindsey and Val Vista is really good. Try the mole. They have a taqueria at the same location if you want something less formal. Los Favoritos for breakfast burritos...I've had a couple bad experiences there at dinner time (food cold in the middle on two visits, for instance).
I'm always looking for new and spicy mexican food restaurants. I'll start out by telling you 2 of my favorites. I really like Los Dos Molinos, it's fairly spicy and the taste is GREAT! For a quick bite I like Los Favoritos Taco Shop. Kind of like a Filebertos but much fresher taste.
So waht are some of your favorite mexican food restaurants? Where are they located? Any one know of any that are REALLY hot and spicy?