I have NIK tools as well as a lot of software from Topaz labs for this but I keep coming back to Photoshop's Unsharp Mask, personally. Mainly because of the degree of flexibility and control it offers. Getting the most out of USM requires you to learn a few simple things but it really puts you in the drivers seat when it comes to sharpening an image once you do. If you can't do what you need to get done using USM it probably can't be done, at least not well. But this assumes you're starting with a good, clean image that can be properly sharpened to begin with.
Another good application many may not have heard of, though, is one called Focus Magic. I don't know if it's still around but it's a great application that works differently than USM. As I recall it's kind of a combination of Adobe's "Camera Shake Reduction" combined with standard micro-contrast sharpening... Or something.