I sharpen most of my images at some point and normally use the “Smart Sharpen” filter in Photoshop or, more usually these days, the sharpening offered by Lightroom. Sometimes, however, I want a very dramatic sharpening effect without the haloing you tend to get with the basic sharpening filters. In these cases, here’s a technique I find rather helpful. This involves the Photoshop “High Pass” filter. Here’s the basic process for it.
You can also use “Soft Light”, “Hard Light”, “Vivid Light” or “Linear Light” blend modes. Each has a similar effect but the depth of the effect varies with each mode.
For another variation on this, try replacing “Filter/Other/High Pass..” with “Filter/Stylize/Find Edges” and use blend modes “Darken” or “Multiply”. This is a less tunable effect and rather dramatic but it can be put to good use in some cases.
I used the High Pass method on these images to give them a bit more punch: