Thomson Reuters Research Analytics has just released a new edition of its Journal Citation Reports (JCR) providing impact factors and other citation and influence metrics for more than 10,000 journals from 83 countries. The University Libraries provides a site-wide license to this database. The citation data comes from the Web of Science, one of the largest and oldest citation databases. JCR is issued in two editions: Science (& Technology) and Social Sciences.
According to the Thomson Reuters press release, a total of 379 journals received their first Journal Impact Factor. Additionally, 37 journals were suppressed due to questionable citation activity. Note that Thomson is now referring to the new edition as 2013 (based on the year that it was released), but all the data is from 2012. In the Journal Citation Reports interface, it is still referred to by the year the data was collected; i.e., the 2012 edition.
Alternately, there are now a number of free web sites that evaluate the impact of journals including Eigenfactor, SCImago, and Google Scholar Metrics for Journals. Consulting these sites is useful in order to cross-check to JCR rankings and in cases where a journal is not covered by JCR.