JCR just announced that the 2007 data for the Sciences and Social Sciences editions is now available. JCR is a tool that examines the impact factor of a journal using citation data from over 9,000 journals, and published meeting proceedings from more than 3,300 publishers in 60 countries.
JCR (access available to subscribed users or affiliates)
Other tools for assessing the impact of journals
Yes , very good.