ROBOTANK  Nice little utility. Takes pictures on lock and unlock of the screen, and allows you to set a time for it to refuse further input after failed password attempts. It can be activated by a global keyboard short cut, allowing for very quick locking. One thing worth noting is that it doesn't use the OS X screen lock (what you'd get if you set your computer to require a password to wake from screen saver), so it requires its own password to be set. Anyway, I prefer it to locking my screen the old fashioned way, and I didn't much mind paying the $2.40 (Canadian) for it.  
(Version 1.1)