ScreenShot Plus uses Apple's tool to do the capturing, but allows you to scale the capture and select a format, jpeg, tiff, psd, and more!
ScreenShot Plus is activated by pressing Shift-Apple-2, You will then have the option of selecting a region on screen, toggle to window select mode by pressing the space-bar. A window will appear showing the captured area. From here you can scale the image and select a format to save in or attach to an email. ScreenShot Plus uses Apple's Quartz for smoother scaling.
Unregistered copies will save images with a watermark.