Cien Agaves has some pretty amazing tacos plus they have a Habanero margarita if you like it spicy. The AZ Taco Festival is this Saturday at the Waterfront in Scottsdale from 10-5. Just about every Mexican restaurant in town will be there.
Since noone has mentioned it : MANUEL's. There are several locations around town. I can personally recommend the locations at Cave Creek & Sweetwater, Phx. ; 28th St. & Indian School Rd.,Phx. ; Broadway west of Hardy,Tempe. Good family atmosphere,fantastic family owned restruant. Reasonable pricing,Large portions,never ending salza & chips and drinks( non-alcoholic). GREAT place to eat!!