ScreenCaptureX will capture either a window, a section of your screen, or the entire screen as a JPEG file by default, and even allows you to add a caption below it if you wish. You can change the default format from JPEG to either PNG or PICT as well, and you can set the default name to whatever you want, and specify a target folder for the files to be saved to. This little app is great for creating web-based tutorials quickly and easily.
What's new in version 1.5
Compiled to work with Lion (OS X 10.7)
Adds the ability to control the number of seconds before a timed screencapture takes place