Features. Lots of features.
Customize nearly every single aspect of the screenshot:
File name (use format codes to make organization a breeze)
Dimensions
Image format/quality
Have IcyScreen take a screenshot of:
The entire screen
Certain sections of each screen/monitor
The active window
Disable the program temporarily if there hasn't been any activity on the computer
Detect and ignore duplicate screenshots
Enable audible/visual warnings, so you know when a screenshot is about to be taken
Have it take action whenever the Print Screen key is pressed
Have it hide itself and protect functionality with a password

... and much, much more.

home Page - http://www.16software.com/icyscreen/