I know these 'deals' don't tend to get a lot of heat but I feel this is worth a mention.
I just traded in Pro Evo 2012 and Battleship for £21 each. I checked the on-line trade checker and it lists them both as £15.80, however when I went in to store I was told that there is an extra 30% on trade-ins towards new releases so they were both worth £21.
They are both on the list of "selected titles" for the 99p deal found here - http://www.game.co.uk/webapp/wcs/stores/servlet/HubArticleView?hubId=183476&articleId=183477&catalogId=10201&langId=44&storeId=10151
But this actually works out as a better deal and you don't have to mess around ordering on-line.
Pro Evo can be picked up for around £10 now so getting £21 trade on it is a fantastic deal.
Picture of the receipt as proof of trade in value - http://i.imgur.com/Nolbf.jpg