A WordPress plugin for uploading images from other websites
This simple plugin creates an admin page with a form that will download media at the given URL to the local server and sideload it into the WordPress media library.
The original impetus for creating this plugin was the fact that WordPress does not have this functionality already built-in. However, I found out later that Windows (and possibly other operating systems) will in a roundabout way accept URLs pasted into the normal file chooser dialog by locally caching the file and uploading it.