This application allows you to capture the entire screen, the active 
window or a selected region. You can set the delay that elapses 
before the screenshot is taken and the action that will be done with 
the screenshot: save it to a PNG file, copy it to the clipboard, or 
open it using another application.

A plugin for the Xfce panel is also available.

You can grab the development version with subversion by running:
svn co http://svn.xfce.org/svn/goodies/xfce4-screenshooter/trunk/ xfce4-screenshooter

The documentation is available in the doc/ folder of the source tree and
on the website: http://goodies.xfce.org/projects/applications/xfce4-screenshooter