Get $25 back when you spend $100+ at Costco.com w/ American Express App for iPhone (no Facebook required)
Same offer , but without having to use Facebook.
Just log into your account using the American Express App for the iPhone [apple.com], tap "Offers Available For You", and you should see the costco offer there.
Be sure to install the American Express App for iPhone even if you are on an iPad, as the iPad version doesn't seem to have these offers on the app.