Disclaimer: I saw this idea listed in another proposal, but it was buried under another idea.
Include a customizable popular posts widget that would enable us to display most popular posts by day/week/month/year; category; tag; etc.
It would also be nice to be able to set the criteria that determine popularity and manually edit the list so that some piece of featured content could be in the list right when it is posted.
In a dream world I would also be able to choose where the data came from, e.g. WP stats, Google Analytics, etc.