After Shutter, the Skitch like for Linux, I would like to spot the light to a very useful Linux app called Caffeine.
Why is it use for?
Caffeine stop your computer for going to sleep, or just to switch your back light off.
Really useful when watching a video, or during a meting.
You can also add process, that will automaticaly enable Caffeine. (Like VLC, OpenOffice, what ever ..).
How to get it?
On the Caffeine developer blog, you can find a good introduction to the software.
To install it, just follow the instructions for the Caffeine Wiki.