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thats a good one! high pass sharpening is really use full
also using the levels and bringing in the black and white sliders on the histogram to where it goes from a flat line and starts to go up (if that makes any sense...) makes a substantial difference
something I do which can add some interesting colour toning is to take a curves layer, pull the curves about all over the place in the red and blue channels, reduce the opacity to <15% and try different blending modes on the curve layer.
layer masks are very useful too
Sharpening with duplicated layer and high pass filter, in addition to changing opacity of the filter-layer, and erasing parts of it.