Tu Casa is one of my favorite standbys. It's good, it's inexpensive, and they bring your meal out in a jiffy. At lunch, $7.75 gets you a huge plate featuring an enchilada, a taco, rice, and beans, with melted cheese strewn liberally about.
And of course, there's the requisite all-you-can-eat chips and salsa (with a decent amount of heat).
It's always way too much food for one person, but then, that's part of the experience. I like knowing when I walk in that I'm going to walk out totally stuffed, with a box of food that's filled with enough food for an entire second meal.
With every entree you're able to choose between cheese, chicken, ground beef, and shredded beef picadillo (which is what I recommend). Some call it Mexican, though others contend that it's more accurately called Tex Mex, it's comfort food in a comfortable setting. And sometimes, that's all you need.