Hi there, I live in Chicago and if you're into museums, the Field Museum mentioned above is wonderful, you might also check out the Museum of Science & Industry or the Art Institute of Chicago. Both are great. There is also Navy Pier right on the lake... it's a pretty touristy spot that has a couple of attractions including a large ferris wheel. You can get really decent views of the Chicago skyline from there. If you're into shopping - Michigan Avenue is the place to go. Below is a list of places you might research before arriving:
The following four are pretty close together and are considered the 'Museum Campus':
1. Field Museum
2. Art Institute of Chicago
3. Adler Planetarium
4. Shedd Aquarium
Grant Park(also part of the museum campus) - Buckingham Fountain, Ptritzker Pavillion
Museum of Science & Industry
Navy Pier - touristy attraction
Willis Tower(formerly Sears Tower) - tallest building in Chicago w/observation level
Michigan Avenue aka Magnificent Mile - shopping
Hope this helps. If you have any questions, please don't hesitate to ask... I'll try my best to answer any questions you might have.
Stephen