Lately I'm using Unsharp Mask on every image (I also set in-camera sharpening off, like Tom).
Just to be a bit special, I apply six consecutive Unsharp Masks on a duplicated layer of the full-size image:

1.  10% at 100 pixels
2.  10% at 50 pixels
3.  10% at 12 pixels
4.  20% at 4 pixels
5.  30% at 2 pixels
6.  40% at 1 pixel

That leaves the image somewhat over-sharpened, but since it's on a separate layer, I can adjust the opacity, normally to about 40% in the Luminosity blend mode.
Oh, it's about the most satisfying method I've tried (I also tried the High Pass filter for a while). Not only does it sharpen images, it also increases the mid-tone contrast. To streamline the sharpening process, I made a Photoshop action out of all this.

After downsizing for the web, I usually apply Unsharp Mask at 40% and 0.3 pixels, and 50% at 0.2 pixels (if needed).

We do not see things as they are. ǝɹɐ ǝʍ sɐ sƃuıɥʇ ǝǝs ǝʍ