Share Selection, Share Pixels
"Share Selection" command quickly copies the existing selection to another image.
1. Open two images.
2. Create a selection in one of the images.
3. Run "Share Selection" script.
In case of more than two images of the same size, the script opens an extra dialog letting you select the target document (screenshot).
If you need to transfer the selected area of the image (as opposed to the selection edges) use "Share Pixels" script instead.