If you join Costco, sign up for automatic renewal, and use an American Express card, you can get two months free. Here is the advertisement.
There are two ways you can do this:
The first option is to sign up for the Costco TrueEarnings Card from Costco and American Express.
The second option is to sign up for automatic renewal of your Costco membership on your existing American Express Card. This can be any American Express card – it need not be a Costco American Express Card (you can opt out of automatic renewal any time in the year). This offer expires on June 30, 2012.
The ad says that you must print out the offer and bring it to any U.S. Costco location.
I let my Costco membership lapse, but this is a perfect incentive to sign up again.