Here are a few more ways for a screen captures and a way to change the Save location and image format from PNG to something else.
Screen Capture:
* Command-Shift-3: Take a screenshot of the screen, and save it as a file on the desktop
* Command-Shift-4, then select an area: Take a screenshot of an area and save it as a file on the desktop
* Command-Shift-4, then space, then click a window: Take a screenshot of a window and save it as a file on the desktop
* Command-Control-Shift-3: Take a screenshot of the screen, and save it to the clipboard
* Command-Control-Shift-4, then select an area: Take a screenshot of an area and save it to the clipboard
* Command-Control-Shift-4, then space, then click a window: Take a screenshot of a window and save it to the clipboard
In Leopard, the following keys can be held down while selecting an area (via Command-Shift-4 or Command-Control-Shift-4):
* Space, to lock the size of the selected region and instead move it when the mouse moves
* Shift, to resize only one edge of the selected region
* Option, to resize the selected region with its center as the anchor point
Or you can use Preview's Screen Capture under the File menu to capture From Selection, From Window or From Entire Screen. Then you can give the screen capture a name, Select the file type and save to the Location of your choice.
ThinkerTool will allow you to change the screenshot image format from PNG to jpg or other formats and save to other locations beside the Desktop.
TinkerTool: Description