You're spot on with Geja's for fondue. No question there.

Lots of good places for steak in Chicago and everybody has a personal favorite. For some people it's Gene's; others prefer the Chicago Chop House, and my personal favorite is Gibson's.

Good variety of theatre options as well if that's your thing. Personal favorites include Steppenwolf and Victory Garden, both of which are close to Geja's if you want to make a night of it, but it doesn't sound like you'd have much time to spare on Friday if you aren't getting into O'Hare until 7:30pm.

Of course, there are the usual suspects -- excellent museums, shopping on the Magnificent Mile, top of the Sears Tower or John Hancock buildings, etc. Not sure what kinds of things you have in mind, but if the weather cooperates and you want to do something off the beaten path and away from the usual weekend tourists on Michigan Avenue, you can always ride the L away from downtown and into a neighborhood like Wicker Park and spend an afternoon walking around looking at the shops and galleries. Things like that are more appealing to me than standing in a queue, but let us know what you like.

A particularly good resource for what's going on in Chicago is http://metromix.chicagotribune.com as well.