OS X 10.8 or later. Append the same user-entered text to the beginning or ending of the existing text in the chosen tag (Song Name, Artist, Album Artist, Album, Composer, Comments, Genre, Grouping or Show Name, and their Sort siblings) in each selected track.
For tags other than "Song Name" and "Show Name", this script may be just slightly less involved than performing a multi-edit on the selected tracks.
Also see This Tag, That Tag.
Preview each track as it will appear after applying the entered text.
Enter text for the selected tracks' Description tag
Re-locate files of selected tracks to new folder, preserve track meta-data
Use tag info from selected track to search Amazon Books for cover art
List tracks not assigned to playlists
Exports and then re-imports selected tracks' artwork
Collect podcast episodes that haven't played thru to the end