Deselect/Reselect

If you're done using a selection and would like to work on the entire image, choose Select > Deselect. When you don't have a selection, you can work on the entire image. Now, if you need to use the last active selection (and there isn't a selection on your screen), you can choose Select > Reselect. This is great when you need to use the same selection over and over again. I use these two commands all the time.