This thread has a lot of good discussion of Mexican spots, especially those with a more pleasant and tidy sit-down atmosphere.
As for pizza... well, there are pizza places in Mexican neighborhoods, of course, and there are fast food places that have both tacos and pizza by the slice, say, but I can't think offhand of a place that does both things well enough to recommend. I think you should eat pizza in pizza places and Mexican food in Mexican restaurants.
Here's a good pizza thread that mentions a number of places.