What's your availability? There are a number of things to do during the day including the riverboat and/or lakefront architecture tours, the Art Institute, the museum campus (Shedd Aquarium, Adler Planetarium, Field Museum of Natural History), Navy Pier (very touristy), Musuem of Science and Industry. There are free admission days (usually Tuesday, but I'm not sure about during the summer), but your best bet on seeing a number of them is with a City Pass. The Art Institute is not part of the City Pass but I can get you in as a member's guest, if you want to do that on Monday or Tuesday.
http://www.citypass.com/city/chicago.html?id=VpWnFsMk
The Grant Park Music Festival has free concerts on Friday and Saturday evenings. The schedule for next weekend is:
Quote:Friday, August 4, 2006 at 6:30 p.m.
Saturday, August 5, 2006 at 7:30 p.m.
Orchestra Hall at Symphony Center - 220 South Michigan Avenue
Grant Park Orchestra; Carlos Kalmar, Conductor; Jennifer Larmore, Mezzo Soprano
KERNIS Too Hot Toccata
BERLIOZ Le Mort de Cleopatre
KERNIS Symphony in Waves
BARBER Andromache's Farewell
Joe - are the concerts still free when they're held at Symphony Center vs Millennium Park?
Other music options include jazz clubs or blues clubs, and there are plenty of music venues around the feature different rock genres.