I’ve just added a Most Commented Recent Posts widget to the sidebar under the Recent Comments widget. The idea is that it will help people find those lively conversations from the last few weeks and keep those discussions going after the posts themselves roll off the front page.
The number of links displayed in both widgets can be tweaked. At the moment I have twice as many links in the Most Commented Posts widget as in the Recent Comments widget, in order to encourage people to not only look at the most recently commented posts. Thoughts?