Tagline Rotator plugin randomly selects a tagline from a list of user-entered taglines.
Update 12-28-10: If you're running an updated version of WP (i.e. 3.0 or later), the plugin may not show your taglines at first. If you deactivate and reactivate the plugin, your taglines should appear. This is due to a change in WordPress that you can read about here. The Tagline Rotator plugin does pretty much what it sounds like it would do: it randomly selects a tagline (that’s the description of your blog beneath the title) from a list of user-compiled taglines, then displays it within your blog. It offers a couple of advantages over some of the other similar plugins I found, most importantly that it uses the mySQL database within WordPress, and therefore should not slow down page loads significantly. As of version 1.1, it is now WP database prefix compliant, meaning it will use the database prefix stored in your WordPress settings, and should be WPMU compliant.