Eigenfactor is a free tool developed by Carl Bergstrom’s lab at the University of Washington. It measures the impact of a journal based on the number of citations as well as journal pricing. They describe themselves as:
(1) Eigenfactor.orgTM scores and Article InfluenceTM scores rank journals much as Google ranks websites.
(2) Eigenfactor.orgTM reports journal prices as well as citation influence.
(3) Eigenfactor.orgTM contains 115,000 reference items.
Eigenfactor.org not only ranks scholarly journals in the natural and social sciences, but also lists newsprint, PhD theses, popular magazines and more. In so doing, it more fairly values those journals bridging the gap between the social and natural sciences.
(4) Scores adjust for citation differences across disciplines.
(5) Scores rely on 5-year citation data.
(6) Scores are completely free and completely searchable.
Read more detailed explanations at http://www.eigenfactor.org/whyeigenfactor.htm
Read a more scholarly description of the Eigenfactor at http://scholarlykitchen.sspnet.org/2008/07/23/eigenfactor/