MacRumors.com

MacBidouille has received reports that Panther will be made available in its final form at Jobs' Keynote at Apple Expo (Paris, France) on September 16th, 2003.

This correlates with an old report from eWeek back in April, 2003:

Now that Apple Computer Inc. has let the cat halfway out of the bag about the next major revision to Mac OS X, sources report that the "Panther" release will reach end users in mid-September.

According to sources familiar with the forthcoming revisions to the Unix-based OS, Apple will freeze development on new features in May and finalize enhancements to the user interface in July.