Over at The Online Photographer (a site that has lately become regular reading for me) a recent post by Ctein linked back to an excellent summary of the benefits of using low-level, high-radius Unsharp Masking as a way to get images to “pop”. This is a technique that I use on almost every scanned image — for lack of a better description, it increases contrast “locally” without making the whole image look contrasty. Ctein explains how it works better than I ever could, though he does use different settings (I typically sharpen at 20% with a 20- or 30-pixel radius, while Ctein uses 8-15% over 60 pixels).
I remember feeling elated when I discovered this technique. It gives images just a bit of an edge without any hint of that nasty over-sharpened or posterized look. You can use it in pretty much any image-editing software that provides an Unsharp Mask tool. It’s simple and definitely worth trying.