KDE's ksnapshot is a deceivingly powerful screenshot application that opens when you press Print Screen. You can directly save the taken screenshot or send it to GIMP or any other image processor for further edits. With the Capture mode field you can select what exactly you want to capture, for instance a specific window or by drawing a rectangle right on the screen to cut the created image. With the Snapshot delay function you can let it count down so that it becomes easier to capture desktop effects or other things in motion.

When Print Screen doesn't work

In older versions of KDE ksnapshot didn't automatically launch. If you have this, launch ALT+F2 and type custom shortcuts. Now under Preset Actions, create a preset that triggers on the printscreen button and use ksnapshot in the command field.