I've been looking for ways to improve my nature photography in particular and ran across these freeware (donationware) plug-ins that I have found quite useful for sharpening images without the artifacts that many "regular" sharpening algorithms impart to my images.
http://www.photo-plugins.com/Plugins/Plugins/The first is Local Contrast Enhancement..
http://www.photo-plugins.com/Plugins/Plugins/Local-Contrast-Enhancement.htmlAnd the second is High Pass Sharpening..
http://www.photo-plugins.com/Plugins/Plugins/High-Pass-Sharpening.htmlHere is an example of local contrast sharpening on a photo of a finch on my feeder, original, cropped and scaled to 50% on the left and sharpened on the right.

There are also some other interesting plug-ins at the site, I suggest you check them all out.