In a recent discussion the need for a frame / border came up. We found this offering from Tech Radar.
Though their page is aimed at Photoshop, they will of course work for any application with layers. Using Blend Modes, some really interesting results can be achieved.
From their page “If you find these useful, please feel free to share this url with others. And don’t forget to upload your results to our Facebook wall!” – so have a look, download them and have some fun !