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.
Applet assists with swapping, copying, appending data between track tags
Append user-entered text to beginning or ending of selected tag of each selected track
Edit basic tags for a selection of mixed-media tracks
Exports and then re-imports selected tracks' artwork
Remove iTunes tracks disassociated from files
Drag-and-drop to convert audio files with iTunes