It has been confirmed that Loolapalooza will be hitting the following cities this summer:

Atlanta; Boston; Chicago; Cincinnati; Cleveland; Columbus, Ohio; Dallas; Denver; Detroit; Hartford, Conn.; Holmdel, N.J.; Houston; Indianapolis; Kansas City, Mo.; Los Angeles; Miami; Milwaukee; New York; Pittsburgh; Philadelphia; Phoenix; Raleigh; St. Louis; San Diego; San Francisco; Toronto; Virginia Beach, Va.; and Washington, D.C

No official itinerary or second stage acts have been announced yet, but should be soon.

Audioslave, Incubus, Jane's Addiction, Queens of the Stone Age, and Jurassic 5 have all been confirmed for the tour.
Cities Announced for Loolapalooza 2003
Source: Billboard