There are a few Starbucks locations I’ve found in Chicago that seem not to have the customary two-hour limit on their AT&T wifi internet connection.

Webster/Clybourn, Chicago
Roosevelt/Wabash, Chicago (Update, 6/9/10: Seems to be limited to two hours now.)
Jackson/Wabash, Chicago (Update, 6/10/10: Seems to be limited to two hours now.)

If you come across another location that gives free wifi internet access for longer than two hours—not just in Chicago, but anywhere—get in touch with me and I’ll add it to the list.