The Google Wallet service is making it's way to becoming the one sore of payment for all things Google. The company recently announced that they will be merging their Google Checkout service to become a part of Google Wallet.Next time you are purchasing an app on Android Market or renting a video on YouTube you will be able to do so using Google Wallet.
The Wallet service will store your address and credit cards and you can make payments by simply using your Google username and password, without the requirement of entering your card information or address every time.
Citibank users have the option to link their cards with the Google Wallet mobile app and make use of the NFC feature on their Nexus S devices to make payments by simply tapping the phone against the merchant's receiver without the need for swiping your credit card or signing.
source - Google