Thanks so much for your response and for the compliment! It's been fun to put this together and learn more about the template along the way.
I'm not sure that the content in the right sidebar is the culprit, because there are pages where the center area has more content than the sidebar. For instance; http://www.cybermill.org/whats-new/news-2/
What else might it be? I've looked through the styling options for the center area, posts & pages, layout, footer, etc - can't seem to find the culprit.
Any ideas welcome!!! Thanks!