You can find a maps of Chicago and the surrounding area on the Google Maps and MapQuest websites. Both sites are free to use, and both provide extra information such as directions and business locations.
If you're looking for a specific location in or around Chicago, Google Maps lets you search for a specific address. You can also search for ZIP codes or more general terms, such as "cafes near Millenium Park." Google Maps can plan routes and give directions, as well as information on transit, cycling routes and terrain.
MapQuest also offers tools for searching and route planning but also features a toolbar that allows you to highlight locations such as hotels, restaurants and gas stations.