This script will export the artwork of the selected tracks, or the tracks in a selected playlist, as an image file to the folder which contains each selected track's file--presumably the track's Album folder--or a specific user-selected folder. If multiple album tracks are selected, the script will make sure only one artwork file per Album is exported.
OS X 10.6 or later only.
Also see Save Album Art as folder.jpg.
This Preferences pane for the script remembers your settings between uses.