Whenever I'm stuck in Schaumburg, I always go to Pancho's Burritos. It's a simple Mexican quickie joint that sells the standards: taco, sope, tamale, burrito, torta, etc. On the weekends they serve an excellent chicken soup concoction with tortillas on the side. I really enjoy their chile rellenos and sopes, especially with cactus and egg. Nearly everything on the menu is cheap and good.
FWIW, I've been up and down N. Clark St. looking for a comparable Mexican place and have not found one that is as good as Pancho's. (caveat: I'm not Mexican, but I've been to some excellent Mexican joints in the Southwest and Southern California.)