Heard about this from a radio ad: The Parking Industry Labor Management Committee has a website, www.chicagoparkingmap.com, that shows parking lot locations throughout Chicago, with info about hours, rates, whether they take CCs (! some don't!) etc. There are both HTML and Java versions. I haven't had to try it out yet, but a quick glance shows that it could be useful for the areas covered.

Caveat: given the source, it may only show the lots that have union-represented workers, and there may be other alternatives, but at least if you are heading to an area you don't know, you'll have a fall-back if nothing else.