You can get $20 off a $50 purchase from the american express facebook page
here: http://www.facebook.com/americanexpress?sk=app_216352075054740
then you can get another $20 off $50 from checking in via foursquare on your
iphone/android phone
I thought they were the same promo until i got two credits on my amex
account
they stack, making it $50 for $10