Apple now allows developers to issue up to 50 promotional codes for each version of any application in the store. The codes allow the recipient to download a full copy of the application. Currently they can only be redeemed in the US app store.
This makes it a lot easier for developers to send out review copies. Until now, it was necessary to build an Ad-hoc copy of any non-free application, which required providing the device ID of any iPhone or iPod it will run on.