Key Ring - I have noticed that many stores that are offering discounts and discount cards.  Many of these stores give you a key ring card with a barcode on 

it to scan at the checkout counter. I have tried a few of these apps that allow you to scan them into your phone and present them to be scanned. The one I really like is called Key Ring Rewards Card by Mobestream Media. Not only does this app offer tons of preset stores to add in but they also offer discounts on products at many of the stores.  Think of it like a card holder and Groupon mixed.  Unlike other apps of this type, Key Ring also syncs to the cloud allowing you to keep the data even between devices.  With coupons offered and over 700 stores preloaded this is a simple replacement to all of those cards.

https://market.android.com/details?id=com.froogloid.kring.google.zxing.client.android&feature=search_result#?t=W251bGwsMSwyLDEsImNvbS5mcm9vZ2xvaWQua3JpbmcuZ29vZ2xlLnp4aW5nLmNsaWVudC5hbmRyb2lkIl0.