Eigenfactor.orgTM scores and Article InfluenceTM scores rank journals much as Google ranks websites.
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:
(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
I especially like their visual mapping search display that animates the relevancy of topics and journals. You can get to this interface by clicking on the "mapping" tab and choosing the "interactive browser" option. In the right side of each visual map result, the top ten journals in that field are listed. Clicking on a journal title will reveal its Eigenfactor score.
The Journal Citation Reports (JCR) is a paid database from ISI Web of Knowledge that the Eigenfactor is comparing itself to, but they claim with added value. View the publisher's tutorial of how to search JCR. (Note: click on the white arrow in the bottom green menu bar to forward to the next page of the tutorial).
Read a more scholarly description of the Eigenfactor at http://scholarlykitchen.sspnet.org/2008/07/23/eigenfactor/