This script will add or subtract a half-star from the ratings of the selected tracks. Ratings with half-stars appear with "1/2" appended to their ratings (see the screenshot). I highly recommend attaching a keyboard shortcut to this script for faster access.
iTunes 6.0.2 or better (I only discovered this in 6.0.2; it may work in earlier versions).
The scripts have also been posted on the Missing Menu Commands page as separate add and subtract actions.
Also see Assign Half-Star Rating.
(Note: In order to launch this PowerPC-era script on an Intel machine, it must first be opened and then saved using AppleScript Editor, which is located in your /Applications/Utilities/ folder. More information is here.)
Move selected playlists to a new or existing folder
Continuously update your desktop picture to current track's artwork
Applet assists with swapping, copying, appending data between track tags
Copy Artist to Album Artist of selected tracks
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
Copy number prefix in Song Name of selected tracks to their track number tag