BioMed Central's blog has a piece on "SCImago – a new source of journal metrics offering a wealth of free data on open access journals." The importance of a specific journal is of interest to anyone publishing their research - obviously, one would prefer to publish in a journal with the greatest impact. Thomson Scientific, as the first to create this metric using Citation Indexing with their Journal Citation Ranking (JCR), has long had the dominant role, but many have criticized their methodology, and been frustrated by their slowness to include new journals. Also, this service is costly.
A few companies have challenged Thomson Scientific's monopoly (Scopus and Google Scholar, for example) and now SCImago has joined the fray. It uses data from Scopus, and gives weights to the citations based on their sources - a citation from a lesser-read journal will have lower impact on the rating than one from Nature or Science.
Thanks, to Jim Craig for bringing this to our attention.