http://en.wikipedia.org/wiki/Pearson_Scott_Foresman
We've had a substantial number of illustrations donated to the Wikimedia Foundation under Public Domain that are presently being uploaded by interns in the office. These illustrations may be found at http://commons.wikimedia.org/wiki/Category:PD-ScottForesman.
I'd also like to point out that a great many of these scans require cleanup (cropping, rotation, inversion, levels adjustment, grayscale conversion, conversion to PNG) and/or categorization, and have been added to http://commons.wikimedia.org/wiki/Category:Images_for_cleanup. These illustrations are a great resource, and many Commons users have already begun to help out in the cleanup process, but I wanted to offer the cleanup opportunity to a greater number of users with graphics skills.