Welcome oldhunter! If you grew up in DuPage County you are probably familiar with Portillo's that got it's start in Villa Park in the 1960's. I know they still have pretty good dogs but Italian beef is my long time favorite there.
I second that. Portillo's is the best, but like kland I prefer the italian beef. I take mine with mozz and hot peppers. You can order the beef to be shipped pretty much anywhere too, and it's pretty darn close to the real thing when you make it at home. Best giardiniera there too!
I do like to get a few jumbo chili dogs from Portillo's too. Can't beat that with a stick.
If you're in the city and looking for some fun with your dog, get a late nighter at Weiner's Circle in Lincoln Park.