My favorite meal of the day is breakfast, and you cannot go wrong having breakfast at Anne Sather’s. Make sure you get some cinnamon rolls.
The West Loop is a neighborhood near Greektown, and would be a quick cab ride or a longish walk. Here are a couple of favorites:
Wishbone at 1001 W Washington is great for breakfast. So-so for lunch or dinner.
La Sardine at 111 N Carpenter has the kind of food your grandmother would make if she were French. They have a prix fixe on Tuesday where you can order any starter, any main course and any dessert off the menu for $20. Reservations a must on Tuesdays, needless to say. Wine (bottles) is half price on Mondays.
Santorini 138 S Halsted is my favorite in Greektown. I’ve been to all of them and Santorini is a serious notch above the rest, in my opinion.
Near the Art Institute at 77 E Adams is Russian Tea Time, a restaurant I’ve gone to dozens of times. It’s truly wonderful, and the flavored house vodkas are great (I’m addicted to the coriander).
For Thai, I’d go to Taste of Siam, which is at Dearborn and Harrison (pretty close to your hotel).
And I’ll second the recommendations for the following:
For pizza, although it is both popular and touristy, go to Uno’s or Due’s. The wait is long, the place is crowded, but the pizza is the absolute best! Middle eatern food, try Reza’s. And microbrews, go to Goose Island. Also, I was surprised to see someone recommend Su Casa. Not because it is bad but because it is one of those “not known” places you asked for. If you like margaritas, this is the place to go. It is right around the corner from Due’s (and owned by Uno’s).