Suggested citation for the current version of the Clements Checklist, including the October 2012 Updates and Corrections:

Clements, J. F., T. S. Schulenberg, M. J. Iliff, B.L. Sullivan, C. L. Wood, and D. Roberson. 2012. The eBird/Clements checklist of birds of the world: Version 6.7. Downloaded from http://www.birds.cornell.edu/clementschecklist/downloadable-clements-checklist 

Download the checklist (Excel spreadsheet, 8.05 MB)

(This will take a couple minutes because of the size of the document.)

If you do not have the Excel program, you can download the checklist in CSV format here.