Apple - What's the quickest way to get a graphic on the clipboard saved to disk?

Maybe the File | New From Clipboard menu of /Application/Preview.app.

Here is a utility to do just that.

pngpaste

Paste PNG into files, much like pbpaste does for text.

However instead of pngpaste > thefile.png, it's pngpaste thefile.png, so one does not accidentally barf binary into the console.

If you have Preview.app open you can simply 'create new' cmd+n and that will generate the proper canvas and paste the clipboard image. Only thing left to do is save that file. Presto!