When it comes to pairing wine and fajitas--a situation that might occur for some people only after every last margarita on earth had been drained--here's a general thought. Fajitas, which are typically served with onions, grilled bell peppers, cheese, pico de gallo, possibly guacamole, maybe sour cream and who knows what other fixings, fall into the broad pairing category of "It isn't the meat, it's the sauce (or condiments)." Essentially, you're picking a wine to go with a mass of wildly different flavors. So you want one that goes with, more or less, anything. There's also a general pairing rule of thumb that suggests matching weight with weight--with a delicate piece of sole, pour a lighter wine; with something like a fajita, pour a wine with more heft. It's a handy guideline, especially when you don't want to think about nuances of flavor.
With fajitas, following these two guidelines, there are a number of reds out there that would work just fine--Monastrell from Spain, Malbec from Argentina, a Grenache-based red from the South of France--but from California, go for Zinfandel.