How to Find a Hotel
The easy, expensive way: Go to your favorite web travel broker (e.g. Travelocity, Orbitz, Hotels.com, etc.) and book it there.
The harder, cheaper way: Use Priceline.com. For airfare, Priceline doesn't really give you a much better deal than any other method, but for hotels, you can sometimes really get a bargain.
If you go with Priceline, it will be more work, because you have to do research to make sure you don't overbid. Goto the BiddingforTravel.com forum and read the FAQ on hotel bidding. The whole thing. Really. (Johnny didn't once and he overbid.) Also read their reviews of hotels in the area to get an idea what the star-ratings mean. Then read what winning bids other people have been able to submit. (Reading what others bid is particularly important to get an idea of what is the going rate since peak times, like summer, is so much higher than off-peak.)
There are many hotels in the Chicago area. Here we list a few we've had experience with in downtown or near O'Hare. See the BiddingforTravel.com Chicago hotel list for a good list of options with links to reviews.
In general, if you're in town for just a day or two, you'll find staying downtown will be much more fun and convenient. There's nothing to do near O'Hare, but we include it in case you want to be near the airport.