The Art Institute has has a "Fashion" exhibit going -- but I just checke, and it leaves September 29, which makes me doubly sad, since I didn't manage to make it there, either.
It's totally touristy, but I always tell people to buy some Garrett's Popcorn. It deserves its fame -- particularly the carmel corn! Make sure you travel far enough south to hit the Macy's on State Street, if you haven't already. I don't shop there much, since I'm still upset over losing the superior Marshall Field's, but I love viewing the fountain, the Tiffany dome and windows in the architecture.
If you like "boutique" type shopping, you'll find some great shops in Wicker Park and Bucktown. And, if you want to really "see" the skyline, take time out for one of the boat cruises -- Wendella or the Architecture tour. I like the ones that go up the river as well as out on the lake, and, when my friends come in to shop, its a nice place to sit for awhile, as long as the weather cooperates!