Northwest Airlines coupon voucher

 
Northwest Airlines PK223 e-cert takes $50 off of your round trip ticket.  This voucher can be used for travel originated within the United States or Canada.  The voucher is good for international travel.  Ticket must be purchased by March 31, 2009.  Travel must be completed by March 31, 2009 also.  There is no restriction to this e-cert, except it does not give additional discount to promo fare.  It does not work with flights that do not operate by Northwest Airline.

You can find them on the internet, such as craiglist, sell.com, etc.