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.)
Export artwork of selected tracks to parent or specified folder
Display, create text file listing info of dead tracks
Remove iTunes tracks disassociated from files
Change video kind and video related tags of selected video tracks
Re-locate files of selected tracks to new folder, preserve track meta-data
Paste non-ID3 Tag track and file related info into Category, Comments, or Description tag