So, my thoughts on the new app in descending order of likelihood.
1) iBooks - A new desktop application that will allow you to read and buy books from the iBookstore, or even your own imported epub books. This will be especially geared toward students, with options such as highlighting, notes, bookmarks, multiple books open simultaneously, and integrated dictionary and thesaurus. You might even be able to write your own ebook within the app, and publish it right to the iBookstore.
2) iPaint - The paint and drawing app you've always wanted for the Mac. etc. etc. etc.
3) FaceTime - A long-shot because iChat is already integrated in the OS, not iLife; but including this in iLife will allow them to update/add it without having to wait for an OS revision.