Giordonos - pizza, mmmmm
Taste, until Jul. 2
Museum Campus, Shedd, etc
Go to Millenium Park - the "Bean", outdoor concert hall, there is a hidden outdoor mini golf course there, you can drink while golfing then sit and eat (watch other restraunts in Millenium Park, they are tourist traps) -- a couple block walk and there are plenty of places to eat
Stop at any divey hot dog joint, they are good
Margies Candies - two locations, look them up it's worth a go. Ice cream, home made candy and home made chocolate sauce to start
Museum of Science and Industry - BodyWorlds is there now....GO

The 95th restaraunt, its not cheap, but ask for a window seat...the 95th floor. Expect $75 a head without booze and make reservations a few days in advance for a window seat especially.
Boat tours are nice if you want to learn. My suggestion is the SeaDog. That one is the best, you are on basically a twin hull speed boat.
Navy Pier is good. Look up what days and times they have firework shows. Otherwise it's not worth going. The show is amazing.
I live in Chicago so PM me if you have any other questions. Just figure weekends will be swamped at any tourist area.
Check out Yelp and find some nice gems too.
Oh yeah fish stores. They are not downtown, but within 10-15 miles of the Loop.
Ocean Design Aquarium, Living Sea Aquarium, and Old Orchard Aquarium.
I frequent these and really I don't need to look anywhere else for nice fish and advice.
Enjoy!