A few more that occurred to me:

* If you know how to sail, rent a sail boat (or charter one with a captain) and see Chicago from the lake.

* The Museum of Science and Industry is a great museum for both kids and adults. If you go, spring for the WOW tour. It's an opportunity to see some of the museum's most popular attractions and how things work behind the scenes.

* Arrive or departing O'Hare around rush hour? If you've rented a car and want to avoid traffic, make a detour to Mitsuwa Marketplace in Arlington Heights. It's a Japanese mini-mall with a fantastic food court.

* If the weather's decent, you owe it to yourself to spend some time on the lakefront. Put on your shoes or rent a Divvy bike, then ask your hotel for directions to the nearest pedestrian overpass or underpass. From downtown, you can safely walk/bike for miles. And if you happen to be in town on Memorial Day weekend, considering Bike the Drive. For five hours, Lake Shore Drive is closed to motor vehicle traffic and taken over by bicyclists.

* Going to visit the Lincoln Park Zoo? Don't skip the Alfred Caldwell Lily Pool. It's a hidden oasis of tranquility among the hustle and bustle of the city.

* During the summer, Chicago is a city of neighborhood festivals and concerts. If a festival is not free, admission is usually $5-10 and often includes live music. Be sure to check out the calendar of Millennium Park's concerts (free, pack a picnic), Ravinia ($$, pack a picnic) and Lincoln Park Zoo's Jamming at the Zoo ($$).