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. Previous universal version available at the link below in the "Info" section.
Also see Save Album Art as folder.jpg.
This Preferences pane for the script remembers your settings between uses.