Hardly a surprise considering the amount of specific retailer exclusive pre-order incentives we see nowadays, it's become a trend. Still, it's worth a mention.
Valve have apparently made deals with retailers from around the globe, the incentives range from money off your pre-order to in-game exclusive content depending on which retailer you pre-order with.
The hotly anticipated sequel to 2007's fantastic Portal is set to release on April 18th in the U.S and the 22nd in the EU so get pre-ordering.