Measures of (Social-Media) Success

Not all tools measure the same kinds of things, so you may find several of these useful for your efforts. In addition, some are useful for measuring your blog's or website's reach, while others assess your mojo on a particular social network. My criteria, writing from the point of view of Socialbrite.org? The tool must be useful, free (freemium versions are allowed) and we had to use it ourselves.