Many thanks to Adrian of Adrian's Images who happened to blog that Google had made their set of NIK filters free so I had a quick look and found they would work with two of the programs I have on the Mac: Aperture and Adobe Photoshop Elements 10, fully in Aperture v3.5.1 and all bar the HDR filter in Elements 10.
It was a quick, though large 600MB+ download, an easy installation followed by a quick online search to see where they could be found in each program.
I gave the filters each a quick look in Aperture and then chose a photo to try out the HDR filter:
The rather insipid original:
A bit of a crop and then a look at some of the many pre-set choices, ending up with 'Deep 1' to give dramatic effect. It doesn't end there as there are many tweeks which can be applied. I used the 'Graduated Neutral Density' controls to finish with complete with a partial rotation of the filter to give more light on the left hand side:
That, for me, brought a dull photo to life with a bit of atmosphere. This was only a quick trial as there are more complex and localised changes which can be made with this set of filters but they will take more than a bit of research plus lots of trial and error to find out how to get the best out of them.