This plugin, when activated, creates it's own sidebar widget with a bunch of stats about your website in it, currently including PR and Alexa rank, with more being added.
It is very simple to get the plugin working on your blog.
- Upload
complete-stats.php to the /wp-content/plugins/ directory
- Activate the plugin through the 'Plugins' menu in WordPress
- Put the widget where you want it in the widgets manager.