Please refer to the following links for new and old version of W-8BEN forms. Both of which are currently being accepted until further notice.
Old W-8BEN Form - https://www.irs.gov/pub/irs-pdf/fw8ben.pdf
New W-8BEN-E Form - http://www.irs.gov/pub/irs-pdf/fw8bene.pdf
Please refer to the below url for instructions on how to complete the new W-8BEN-E Form
http://www.irs.gov/pub/irs-pdf/iw8bene.pdf