Never made it to Old Jerusalem in all my years (17) in the city, but there are loads of other great Middle Eastern places in the Andersonville neighborhood; Cousins, Andies and especially Rezas come to mind, all on Clark Street.
Of course Chicago pizza and hot dogs have been mentioned a lot, but some other nominations that I would make:
Buffalo Joes, Evanston. Best burger/dog/chicken wing place in the area overall, IMHO. Great polish sausages, excellent burgers and awesome wings, always a wait but worth it.
Potbellies, several locations. Small sub sandwich chain with excellent bread and quality fillings — and cheap.
Carmens, Evanston. Best stuffed pizza in the area, though Uno and Due are certainly in the running; I just think Carmens’ crust is a little better. I also like Edwardos (another small local chain) a lot.
Golden Apple. Probably the best 24-hour place in the area.
The Lantern (I think thats the name, someone please confirm!) in Lake Forest, best burger I ever had in the area, though it was years ago I still remember, lots of choices, kind of expensive for burgers but worth it — right near the Metra station.
Russian Tea Time downtown near the Art Institute on Adams. Definitely not roadfood prices, I once spent $55 for lunch for two, but a not-to-be-missed experience of Czarist Russian splendor. Great vodka and caviar selections, amazing pierogis, very good vegetarian plate.
Michaels. Hot dog stand, last I was aware they had two locations, on the Gold Coast and in Highland Park; when I worked in the latter (rich northern suburb) I ate there a couple of times a week. Amazing baked potatos, great great burgers and dogs, wonderful milkshakes.
And I will second (or 3rd or 4th or..) previous mentions in the forums and by the Sterns of Mustards Last Stand, Original/Walker Brothers Pancake House, Hackneys, Superdawg, many others. Chicago is truly a great great roadfood town and is blessed with a wonderful assortment of ethnic restaurants (especially Middle Eastern, Chinese, Polish and Italian) and fine dining choices as well. Anyone know the name of the little Polish dive right next to the Gateway theater on Lawrence? Can’t for the life of me remember.