This guide is intended as a resource for citation analysis.
There is no single tool that can give a complete picture of any author's contribution to a field, so its important to make use of the variety of tools available in order to get better understanding of their impact. When determining an author's research impact, it is important to not look not only at the number of articles and/or books that a researcher has published and the ranking of the journals in which their articles have appeared, but also how often those publications have been cited.
H-Index will help you calculate an author's h-index, an idea proposed by physicist Jorge Hirsch to be used as a tool to determine an individual's scientific research output.
Metrics will help you determine the ranking of a journal, the journal's usage, and also provides alternative metric methods such as how often an author has been cited in less obvious places, like blogs or Wikipedia entries.
Resources will give you a list of websites and articles on this subject that might be of further interest.