Brunch in the loop
Let's start out with a list of IMHO the best options...
In the Loop itself, or within a few blocks walking distance:
Atwood Cafe - www.atwoodcafe.com
South Water Kitchen - www.southwaterkitchen.com
Orange on Harrison - http://chicago.menupages.com/restaura...
Lou Mitchell's - www.loumitchellsrestaurant.com
David Burke's Primehouse - www.brguestrestaurants.com
1-3 miles away:
Bongo Room (South Loop and Wicker Park) - http://chicago.menupages.com/restaura...
Between - www.betweenchicago.com
NoMI - www.nomirestaurant.com
Seasons - www.fourseasons.com
The Greenhouse at the Ritz-Carlton - www.fourseasons.com
North Pond - www.northpondrestaurant.com
Kitsch'n River North - www.kitschn.com
I've been posting detailed reports on my brunch visits in the brunch discussion at http://chowhound.chow.com/topics/364403
Here are additional notes, plaudits for my very favorites, and a few caveats...
Some of these places - Orange, Bongo Room, Lou Mitchell's, Kitsch'n - don't accept reservations and waiting times to be seated on Sundays can be lengthy. (All of the others accept reservations.) These are the least expensive of those mentioned here; all are pretty much egg-and-pancake places. My favorite place among this group is Bongo Room. (I've only been to the South Loop location, but I assume Wicker Park is similar.) I really love their pancake dishes, many of which consist of a flavored pancake accompanied by a sauce. One of the best pancake dishes I've ever had was their blueberry pancakes with almond panna cotta sauce. What I also love is that, in addition to their standard portion size of three pancakes, you can order smaller portion sizes of one or two pancakes at reduced cost, which makes it easy to try several different dishes.
Other places - NoMI, Seasons, the Ritz, and Burke's - are fairly expensive restaurants located in luxury hotels, and all are all-you-can-eat brunches. Of these, my favorite is Burke's, for a couple of reasons. One is that it is significantly less expensive than the others ($35/pp vs $50-60), yet I think the quality is at least as high. Another is that I really enjoy their "American dim sum" approach to brunch, bringing the various items to your table, as plated items which are made to order as well as a couple of courses which are selections from carts, rather than having to get up to serve yourself from a buffet.
The remaining places - Atwood, South Water, Between, and North Pond - are a la carte places with a special brunch menu, and generally falling in between the previous two groups in price. In this group, my favorite is Between, because the food has been fantastic on the several occasions I've gone there. Honorable mention, though, goes to North Pond, whose location in the middle of Lincoln Park is exquisite (although it's a bit more comfortable to get there during seasons other than winter).