Picked up a leaflet at Gamestation the other day offering an extra £5 on the trade in price of any Xbox 360 game against Left 4 Dead2
If you use the CEX offer of PES 6 for £1 you will get a minimum of £4 off http://www.hotukdeals.com/item/527916/pro-evolution-soccer-6-xbox-360-1-0
Small print (in image) reads:-
£5 extra trade-in will only be given on one xbox 360 game towards one purchase of Left 4 Dead 2. Any additional games traded in will be at the normal Gamestation trade-in price. Trade-in prices are subject to the inspection of the complete product. Gamestation will beat an higher offer made in the last 24 hours by £1. Trade-in offers are open to members of the public only and Gamestation reserves the right to refuse any other believed to be representing a trade buyer. The managers decision is final. While stocks last. Not to be used with any other offer.