The $7 RecognizeMe by Apocolipse unlocks your jailbreak iPhone by matching pre-recorded images of your face against the front camera feed. Simply holding the device in front of your face for a couple of seconds should automagically unlock it.
Engadget reports that the program works as advertised, albeit with a lot of room for improvements in performance and facial recognition departments. You can set verification threshold in settings and use Face Trainer to improve accuracy. There are literally dozens and dozens head-turning tweaks for jailbroken iPhones but RecognizeMe is without any doubt one of the more original.