I've read over the list of restaurants people suggested, and as somebody noted above, all are excellent (although there are a few new ones I haven't heard of). But the best meal I ever had (and I've eaten at some great restaurants around the world (mostly the U.S.)), was at Charlie Trotter's. If you can only go to one restaurant in Chicago, go to Charlie Trotter's. And if you are daring, see about reserving their "Kitchen Table." It's a table that seats 4 or 6 and is in their immaculate kitchen. You get to watch as Mr. Trotter holds court.