I have slotted this in as an afternoon post because of the small number available, and because Amex has already been promoting it via Twitter today.
Amex and Foursquare are offering £10 cashback when you spend £10 at Dixons Travel (ie £10 for nothing if you can find a £10 item, perhaps an iTunes gift card?).
Your American Express card needs to be linked to Foursquare to activate this – see this post for instructions on how to do it.
You then need to search for Dixons Travel at your nearest airport and hopefully the offer will come up. Click ‘Load To Card’ and you’re done.
If you open multiple Foursquare accounts at different email addresses, you can register multiple American Express cards (assuming you have multiple Amex cards!).
As I said, only 500 card registrations will be accepted. Full details are here on the Amex website. The offer ends on 12th January, so please do NOT sign up unless you are 100% certain to be passing through an airport with a Dixons Travel before then.
Head for Points readers can easily fill all 500 slots on their own, so you are probably hurting a fellow reader if you sign up and then do not redeem the offer.
(Thanks to Antoinette)