I've just added a new feature via a Moveabletype plug-in called 'RelatedEntries', written by Kalsey Consulting Group. On each individual archive page (the one you get to by clicking the posting date of an entry on the main page), there is a list of four entries which share the same category. I'm not sure whether these are randomly chosen—it isn't clear from the documentation. The current items in this section all seem to be rather old, but I suppose it does give readers a sample of stuff buried in the archives that they might not otherwise come across.
I've also fixed a few problems with the templates for the individual archive pages and the 'About' page, which meant that the sidebar drew at the bottom of the page, underneath the main content. I've only just figured out what the problem was, but it's fixed now.