FX-Foundry/Photo/Enhancement/Maximize Local Contrast...
Like Stretch Contrast, but instead of using the minimum and maximum pixel values from the entire image, uses the minimum and maximum in the vicinity of a pixel to compute its new value. Takes a while to run, but really brings out textures. Result is a Grain Merge layer that adjusts values of the original image.
This filter operates on the visible image, not on a layer or selection.
Radius indicates how wide a pixel's influence is. If you choose too small a value, adjustment will be too localized and the image will look patchy. Larger values take a bit longer to run.
Threshold indicates how many neighboring gray values above and below a value can be treated as the same, in finding minimum and maximum values. Purely a speed trade-off. Using very low values will make it very slow. Too high values will cause visible "steps" in color values. The latest version does not include threshold, but the older version is still available.
"Feather Haloes" helps smooth out haloes around high-contrast areas.
"Keep Min and Max Layers" leaves the intermediate layers in the stack so you can look at them if you're interested.
Update (21 Jul 2009):
Updates (13 Jul 2009):
Updates (9 Jul 2009):