I was at the University of Illinois for many years and since then have never found a place with cookies as good as The Cookie Jar has. Hands downs, best cookie is the Buttercreme Sandwich. It obviously can't be that healthy for you, but what do you expect?
The other cookies are just as good, I remember when I was there they had Reese's Pieces cookies that were incredible and unique. The cookie cakes are the best cookie cakes I've ever had, better than any mall cookie shop.
If you are ever on Sixth Street, make a quick stop inside, say hi to Ed (nicest owner in the world), and buy as many cookies as possible, you won't regret it.