In addition to showing the current image "APOD Viewer" also lets you see the accompanying explanation by simply clicking the image. Furthermore it can be used to browse the archives and can show a random image.
The widget has a simple and compact user interface. It is resizable to fit any screen size and provides you with easy keyboard shortcuts for easy interaction with the widget.
This is not the first APOD widget made, but download and try it to see why it, as one reviewer commented, is an APOD widget done right.