Chicago, IL + Add a trip

All Chicago Public Libraries have unlimited free wireless internet. The catch - you must have a library card, but if you are staying with a friend who is a resident, just ask to borrow theirs. All Panera Bread locations and Peet's Coffee locations have free internet with purchase (Panera is unlimited except during the lunch rush, 11-2, when it's 30 minutes only, and Peet's is good for two hours). Virtually all independent coffee shops here have internet access as well. There won't be many downtown, but Intellegencia on Broadway and Belmont is a good one, as is Humboldt Pie on Augusta and California.

I can't speak in general around the city, but if my neighborhood is any indication then you'll find it in almost every coffee shop, and some restaurants. Within 2 blocks of my house (near Fullerton and Clark) there are 2 coffee shops that let you use it for free (no purchase necessary), a coffee shop that gives you unlimited access with a purchase, and 2 more that give you 2 hours of access with any purchase. Then there's 2 restaurants and a pub which all offer free access, though you'd have to buy a meal or drink. Of course, there's also Starbucks, who give you access if you have a coffee card with them (which costs money, but the internet is free).

I work from home, but I spend more of my time at the local coffee shops because the internet is almost as good, and I get to drink coffee while I work. Probably my favorite spot for free internet is The Noble Tree. No purchase necessary, good coffee, and the most comfortable venue around. http://nobletree.tumblr.com/

Caribou Coffee is another good alternative for free wi-fi. There are several around the city and in the loop (Ogilvie, for example). Also the Inn of Chicago Hotel (off Michigan Ave on Ohio - 162 E Ohio) and Doubletree Hotel (a block east from Inn of Chicago) both have free lobby wi-fi access.

In the downtown areas, Chicago offers free public wifi.

Nowadays, any Starbucks, Panera Bread or Staples offers free WiFi. Even Denny's.