La Tapatia (behind Exxon, just off of HWY6) is really good, as well. We've started going there more than Casita because La Casita can be hit or miss, in my experience.
Another old standby that used to be kind of scary looking (but with really good food) is Chela's on BUS6 (aka South LaSalle). They've recently torn down their old building and put up an entirely new stone restaurant. I haven't been since the rebuild, but some friends went and said it was great - same tasty food, much more inviting atmosphere.