Rental Cars at Chicago Airports
    This is part of the travel-information for ASA 2011.
    Below you'll see screen-shots of searches of search-results in Orbitz (done April 26, 2011) to rent a car for 1 week (Thursday, 2:30 pm July 28 to 2:00 pm August 4) at O'Hare Airport (notice the link to let you "see all 76 car options") followed by the same week at Midway Airport where a car costs more with fewer options - or maybe some options are not being shown in this search.
    You can do your own search using Orbitz, or check iFly (as in the third picture below for O'Hare) or travel-ticker or Hotwire, for O'Hare Airport or Midway Airport.
    Or google [chicago o'hare rental cars] or [chicago midway rental cars] to check individual websites.

    TIMING — Here is a comment/complaint about O'Hare Airport, from ifly.com:  "If you arrive at O'Hare, have luggage to claim, and plan on renting a car (you need to wait for the rental car shuttle bus to outside airport locations), count on 1.5 hours."

Because renting at airports is more expensive, probably you can get lower prices by trying other locations in the Chicago area, locations where you could travel to using public transportation in Chicago or private transportation such as a taxi.

O'Hare Airport - using Orbitz

Rental Cars at O'Hare (from orbitz)

 Midway Airport - using Orbitz

Rental Cars at Midway (from orbitz)

 O'Hare Airport - using iFly

Rental Cars at O'Hare (from iFly)