Just spotted this on MSE so can't take credit myself.
Sign up for a Barclaycard Platinum* credit card before Monday 22 October, and you'll get a voucher worth £50 when you use it to make a purchase. This can be used in M&S, Argos, Currys/Dixons, John Lewis, Boots, Debenhams, River Island and Next. This deal isnt available everywhere, only via certain websites it has deals with (this link takes you through one of them).
Simply spend any amount on the card once it comes (make sure you do it before 30 November 2007) and you'll receive a form asking you to choose which shop you want a voucher for. Fill it in and return it before 31 December 2007 to bag your freebie.
There is nothing special about asterisk (*) attached to Barclays Platinum so don't worry there is no fine-print :)