The Annual Printer's Row Book Fair in Chicago is this coming weekend, June 9-10th. All fair events are free and all authors are required to stay an hour after their appearances to sign books. It's going to be great fun, I'm going with my book club.
The site (here) has information on traveling there, event schedules, and a list of authors, as well as a FAQ section.
I'm especially excited to see Audrey Niffenegger as I just finished her book, The Time Traveler's Wife (which I will be reviewing soon).