Last week Arabella posted a link to an article on this subject. The November 2012 issue of College & Research Libraries News has a useful article that describes the various methods for measuring research impacts. See From bibliometrics to altmetrics: A changing scholarly landscape. It describes resources such as Scopus, which we subscribe to, as well as free resources such as Google Scholar Citations. Relevant organizations and networks are also listed. It’s worth a skim at least.