This script uses the UNIX qlmanage command to display a Quick Look window of the selected track(s), which can be audio, video, and, perhaps most usefully, PDF, whereby Preview.app is not necessary. Also handy for playing a single track out of playlist context. Need I add that a keyboard shortcut makes this very handy.
Caveats: 1) under Leopard a media file will begin playing immediately, so the script uses a hack to prevent this, 2) under Snow Leopard and better the QL window's title contains "[DEBUG]" which cannot be suppressed, and 3) the QL window can only be dismissed by clicking on its close box.
Append the BPM to the beginning or ending of the Song Name of selected tracks
Re-locate files of selected tracks to new folder, preserve track meta-data
Perform search-and-replace on text in your choice of tags
Sort purchased tracks into discrete playlists by name or account ID
Append user-entered text to beginning or ending of selected tag of each selected track
App displays files in iTunes Media folder which are not in iTunes library