Here's a little technique I learned from a great photographer called Rob Hanson and it uses a combination of Unsharp Mask techniques.

This works for Photoshop and similar programs. Once you have finished processing your image do the following to sharpen.

First we'll start with Low Amount, High Radius (LAHR)

1. Select All, Copy Merged and Paste as New Layer
2. Use the Unsharp Mask and set the Amount to about 25% and the Radius to about   30

You should notice an increase in sharpening but more importantly, an apparent increase in Contrast

Now we are going to add a High Amount, Low Radius (HALR)

1. Select All, Copy Merged and Paste as New Layer
2. Use the Unsharp Mask and set the Amount to somewhere between 100-150% and the Radius to somewhere between 0.8-1.2

Keep it real here. I usually start with 100 and 0.8 and slowly adjust the radius, but it's up to you, just don't oversharpen to the extent that you get loads of artifacts and funny edges.

If the images don't show too well ahve a look at them on my FlickR Lightbox

http://www.flickr.com/photos/deeferthedog/6812361653/in/photostream/lightbox/

Mike