Screenshoter is a basic screengrab tool that will capture images at the click of a button.
The interface isn't exactly pretty, but then Screenshoter is more about simplicity and speed, and here it works very well. So once you launch the program, you can minimise it, and every time you press PrtSc a grab of your full screen is saved to the desktop (it can generate an automatic file name for you), no other setup required.
If that isn't quite enough, though, you can customise Screenshoter in various ways.
You're able to save the active window and selected areas as well as full screen grabs, for instance. There's an option to include the mouse cursor in your captures. You can choose to save the grabs in JPG, PNG or BMP format, and it's also possible to specify a destination folder if the desktop isn't convenient.