Best Western has a targeted promotion for a free night certificate after just one stay. This offer is valid for stay between February 11 and April 14, 2013, worldwide, but your Best Western Rewards account address has to be in United States, Canada, the Bahamas, or the US Virgin Islands. You can access this offer here.
EDIT: If you didn’t receive this offer directly from Best Western, it might not be possible to sign up for the promotion online. Please call the Best Western Rewards customer service. They can sign you up manually.
Note that the valid stay for a free night can be at any Best Western hotel worldwide, your account address needs to be in United States/Canada/Bahamas/US Virgin Islands, the free night voucher can be used in the United States/Canada/the Caribbean, and that the free night voucher expires on June 30, 2013.