http://twitter.com/mattparker tipped me off to this cool iPhone app yesterday. IntelliScreen allows you to view upcoming appointments, new emails, new SMS messages, the weather forecast, etc on the "slide to unlock" screen. It is very handy to have this information for quick checks without unlocking your iPhone and opening applications.
To install the application, you must have a jailbroken iPhone. Just launch Installer and search for "IntelliScreen." The current version is beta and will expire on June 10th, 2008. My guess is the developer plans to release an official application in the new iPhone App Store around that time.
For details on IntelliScreen check out this web site: http://www.intelliborn.com/.