No 6. WP Health System

This plugin displays the basic server info and WordPress PHP memory usages. It also displays information on the current database utilization status. It also introduces a Dashboard subpage, Memory Usage information at Admin Footer and if permitted Server Storage Quota at Dashboard.

Go here to download.

No 5. Janrain Engage

This plugin allows your visitors to register and login to your site via external accounts such as from facebook. It also allows the visitors to post and display their activities and comments on your blog on facebook and other social networking sites.

Go here to download.