An alternative and free source of metrics is Google Scholar.
To use the citation analysis option in Google Scholar, you will need the Publish or Perish software, which is available for free download at http://www.harzing.com/pop.htm.
Publish or Perish interrogates Google Scholar for raw citation details which are then analysed for the following:
More information on Publish or Perish:
Slideshare on Citation Analysis by Anne-Wil Harzing of the University of Melbourne.
The Publish or Perish software can also be used with Microsoft Academic, which is an alternative to Google Scholar. Microsoft Academic can be accessed at http://academic.research.microsoft.com/.
To use Microsoft Academic, you must register an account.