This script checks your entire iTunes library for missing and presumed dead tracks--those tracks that iTunes is unable to associate with a file and which are listed in iTunes with a "!"--and can create a text file listing these tracks by alleged File Path (if available), Song Name, Artist and Album, which you can view using TextEdit.
OS X 10.6 and later only. Universal version for PowerPC machines available at the link below in the "Info" section.
Also see Music Folder Files Not Added.
iTunes can't find the files pointed to by the Location property of these track entries.