Note: Many open access journals are pulling quite decent impact factors. For instance:

• BMC Bioinformatics - 3.028
• BMC Medicine - 5.750
• BMC Biology - 5.203
• BMC Genomics - 4.206
• BMC Plant Biology - 4.085
• Breast Cancer Research - 5.785
• Molecular Neurodegeneration - 5.361
• Nucleic Acids Research - 7.836

On the other hand (top tiered journal-CNS, but not open access):

• Cell - 32.401

• Nature - 36.101

• Science - 31.364

• PNAS - 9.771

http://www.library.illinois.edu/blog/bicnews/archives/2011/06/2010_impact_fac.html

The 2010 edition of Journal Citation Reports is out, with the 2010 Impact Factors for journals that are tracked by Thomson Reuters (Web of Science). From their news release:

“The 2010 release features the largest ever JCR with 10,196 journal listings in 238 disciplines of Science and Social Sciences. 2,494 publishers from 84 countries are represented, some for the first time. A total of 1,075 journals receive their first Journal Impact Factor in the latest JCR release.”
News Release: http://thomsonreuters.com/content/press_room/science/JCR-impact-factor-2010

Access the Journal Citation Reports database:
http://www.library.uiuc.edu/orr/get.php?instid=258273

Not sure what Impact Factors are? Here’s a link to a presentation I’ve used for a Library Savvy Researcher workshop on the topic:
http://www.library.illinois.edu/export/biotech/docs/ImpactFactors.ppt