Google Checkout

Google Checkout is an online payment processing service provided by Google aimed at simplifying the process of paying for online purchases. Users store their credit or debit card and shipping information in their Google Account, so that they can purchase at participating stores at the click of a button. Google Checkout also offers fraud protection, as well a unified page for tracking purchases and their status.

Below link have Google Checkout API Documentation

http://code.google.com/apis/checkout/

Here is the sample Google Checkout Custom Control link

http://www.c-sharpcorner.com/UploadFile/jlf0002/googlecheckoutcustomcontrol08072006134735PM/googlecheckoutcustomcontrol.aspx