One breakfast and one dinner is all I can fit in during a day in Chicago, so that's what I can report on. I was wandering around Lincoln Park during the early part of the day and stumbled into Nookie's Too (2114 N. Halsted), an excellent choice for breakfast/brunch. A plate of "Dixie Benedict" (poached eggs on ham and biscuits, with gravy) filled me up all the way to dinnertime. Good coffee, reasonable prices, and a nice place to sit at the counter.
For dinner I checked menus at a bunch of places suggested earlier on this board, and ended up eating at Blackbird--mainly because after I had walked there all the way from the Loop, I was so exhausted that I had to sit down. I sat at the bar and had a fine dinner: amuse-bouche of bay scallops over squash puree, starter of sunchoke bisque (super yum), entree of arctic char over peeky-toe crabmeat and marinated (cold) green tomatoes. Excellent bread is served, a sort of multi-grain affair with a nice crust. That and two glasses of cabernet were enough for me. Sitting at the bar worked very well--the bartender was a great server, and I ended up having a nice chat with someone who was waiting a long time for her friend to show up.
Thanks to DBird for this suggestion.