Amazon has just released a significant update to their Amazon Mobile app. The new 1.5 version brings a new level of support for Windows Phone 7.5 (Mango) and a new barcode scanner that can check pricing and availability of an item from Amazon. You can pin that barcode scanner to the Start screen as a Live tile so you can instantly start scanning while you are shopping.
The update also brings support for task switching that is in the 7.5 release.
The update is free in Marketplace and does require Windows Phone 7.5 to be on your phone.