Lots of prizes - e.g. TVs, holidays, free tickets, laptops, hampers, cameras etc
From the website:
This year celebrate Christmas in style with MasterCard. Simply use your MasterCard between 1st - 31st December 2008 (inclusive) then fill out your details to enter the prize draw and be in with a chance of winning any one of the 24 fantastic prizes in the MasterCard Christmas Countdown.
Terms and Conditions here: