I really liked the "Top 10 Posts" on Jeremy Zawodny's Blog and wanted it for my blog as well. So I wrote a small hack which keeps track of the number of times a particular post is clicked on (using the database) and then makes a list of these posts along with the number of clickthroughs. You can see it in work on the sidebar ( http://dinki.mine.nu/weblog/ ). Here is a link to the hack instructions. This is WordPress 0.72 and 1.0+ compatible.
Also, to give my "Who is Online?" hack a little more exposure, here are the instructions to display the number of users on your site at any time.
http://dinki.mine.nu/word/b2-img/whoisonline.txt You can see it at work on my blog http://dinki.mine.nu/weblog/ (look at the "other" area)