FARIBORZ  This is really a nifty utility that can be accessed either by menu selection or via a hot key to hide your screen from curious eyes. Black and white colors fade in and out in a very smooth and elegant way. The price is right and its author has full trust in his customers i.e. no serial number or software key is needed. I gladly paid for it after a few minutes of testing its features. Highly recommended! Fariborz AMIRSHAHI - Verona (Italy)  
(Version 1.3)

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)