Thomson Reuters have just released the 2010 Journal Citation Reports which provide a variety of journal bibliometrics, including the Impact Factor.
To access the JCR, click on the link on the Library website www.lshtm.ac.uk/library/databases/databasesall.html and logon using your network username and password (DL students can logon using your UoL Portal username and password). Once logged into the Web of Knowledge, click the Additional Resources tab at the top of the screen and choose the Journal Citation Reports.
The JCR now includes over 10,000 journal titles, and the 2010 edition provides metrics for over 1000 new titles. Remember, as the 2010 impact factor is derived from citations received in 2010 to articles published in 2008 and 2009, any journals included will have to have been published since the start of 2008.