I've been having really good luck with this website http://spothero.com Spot Hero has allowed me to park at various Chicago hotels for nearly 45% off what the hotel wanted. Spot Hero has also come in handy for parking in the Loop for events/shows, like just last night, I used it while Mrs Sweet Willie & I attended Book of Mormon at the Bank of America Theater. A nice feature is that spothero was able to get me into parking garages/lots that were listed as Full, one is guaranteed a spot if one has a reservation through spothero. Great site, check it out! Just for the record in case someone thinks this is a shill posting, I do not work for spothero, I do not know anyone who does, nor do I gain financially from spothero or parking in Chicago.